There are rumors about a dwarf who is aiming to create a swimsuit. It's equipment, similar to Nazarick's swimwear, and may have come from players. The Pleiades and others were ordered to investigate, but for some reason, Blue Roses was also on the scene--
The protagonist who was stationed in E-Rantel, reports to Momonga via [Message] of urgent news concerning a dwarf who is looking for materials to create a certain equipment---the swimsuit. Having previously encountered a situation where swimsuits were used by the Pleiades to explore a mysterious island, Momonga understands the seriousness this revelation brings. It was originally believed that swimsuits were not known to exist in the New World, but judging from the characteristics and descriptions of this dwarf's work it seems very similar to what Nazarick has in its possession. While there are examples of various household items existing in this world, the dwarf's knowledge about swimsuits may indicate that he is either a player or was in contact with one. The dwarf's location is already pinpointed and Momonga is informed that the dwarf appears to also be in a trade deal with the Re-Estize Kingdom. The situation needs to be quickly addressed as Momonga fears of a possible information leak to the Kingdom. Thus the protagonist is ordered to go find the dwarf and confirm the craftsman's potential threat level. After ending the [Message], Momonga has Albedo summon Demiurge to determine what kind of reinforcements should be sent to handle a possible player. All of the Pleiades are deemed to be most suitable for the task.
At the same time in Re-Estize, Lakyus Alvein Dale Aindra is given a request from Renner Theiere Chardelon Ryle Vaiself. The princess explains that a dwarf by the name of Tsuibayaya had moved to the seaside village a few years ago from his original homeland, but since then has entered into a contract with the royal family to produce high-quality armors for the Kingdom several times a year. The deadline for the retrieval is approaching and the princess would like Lakyus's adventurer team to pick up the armors. Lately the threat of Chaos Beasts has been looming over the soldiers minds and they are showing signs of losing confidence. These armors will help motivate them in their duties and also ensure less casualties. Blue Roses is the only group the princess would entrust with securing the products for the Kingdom's soldiers. While Blue Roses is normally assigned to E-Rantel, Lakyus knowing fully well that armor is in short supply agrees to assist in this mission for the Kingdom.
As for Nazarick, after the protagonist met with Yuri Alpha and received equipment loaned from Momonga, the team is in a carriage traveling to their destination. The mission will be focused on the priority of searching for the source of the swimsuit item. The Pleiades, now his companions, the protagonist and Yuri go over their plan to survey the village and the dwarf. To do this a vigilance team will scout the area and fight off any threats. To observe the dwarf a monitoring team will also be set up to watch from a distance. And finally the contact team will go directly to the villagers to gather information on the dwarf. The contact team would of course be composed of members who have experience in interacting with humans and have human identities such as the protagonist, Slimeko aka "Surako," Solution Epsilon aka "Soi" and Narberal Gamma. Yuri and Entoma Vasilissa Zeta are designated as members the vigilance team. While CZ2I28 Delta and Lupusregina Beta serve as the monitoring team. The mission is deemed to be a simple one by Soi as she believes that it will be easy to find a dwarf in a human village. Entoma using her summons reports that the village they are approaching is being attacked. Rushing outside the carriage, Lupusregina and Shizu confirm that contaminated goblins are attacking the villagers at the gate. Though it is unexpected, the protagonist decides to lead an attack to help the villagers as it will be easier to gain their trust. The contact team then engages and finishes off the demi-humans. The villagers are thankful of the intervention, though state that they had the battle in control thanks to their weapons. After being allowed to examine one of the villagers spears, the protagonist and Soi notice it to be a good quality weapon. It is due in part of the craftsman dwarf who resides in the village. The villagers explain that the dwarf came to their little community years ago, and offered to make tools for free to be allowed to stay, In addition he helped many of the villagers in the militia with training and even became good friends with the chief.
To explain their presence the Nazarick contact team state that they came for the dwarf's work in armor which the villagers accept as true. The villager mentioned how the dwarf was very interested in the local Legend of the Mermaid ever since he arrived at the village. They are interrupted when Gagaran from Blue Roses calls out in recognition. Entoma who had noticed the other adventurers approach had informed the contact team from afar via [Message]. The adamantite adventurers are surprised that the protagonists and his team are present in the village. Evileye taking notice of Narberal, inquires on her identity. The protagonist allows an introduction between Blue Roses and Narberal explaining that she is a fellow adventurer and their purpose is to seek Tsuibayaya for new armor. The adamantite adventurers buy the story, but before the two teams could ask the villagers about the whereabouts of the dwarf, they are distracted by the appearance of more goblins.
After defeating the feral goblins, the two adventurer teams learn from Tina, Tia, and Surako, who ventured into the village during the commotion, that finding Tsuibayaya will not be easy. According to the villagers the dwarf said he had an appointment to meet someone and left, but that was several days ago causing many of the villagers to become worried. The protagonist wonders whether or not the dwarf's disappearance is related to the swimwear. Lakyus is in distress upon hearing the news as Tsuibayaya should have met them by now to give them the prepared armors. It's assumed that the armors are locked in the dwarf's home, but Lakyus cannot take them without permission, so she opts to locate Tsuibayaya. One of the villager speaks out and says that Tsuibayaya had been heading towards the beach on the day he left. Blue Roses believes that Tsuibayaya may have been following on the local legend of the village in which according to the villagers there is a cave that connects to the seaside under the cliffs where the mermaid lives. However, it is taken as just hearsay. The seaside is a dangerous place to go as monsters live there, hence an iron gate was placed at the entrance of the cave to keep them out. No one is allowed entry there without permission from the village chief.
The seaside being a start for their search, they group head to the cave. Just as the villager stated there is a gate at the entrance, however, the locks of the gate appear to be untouched, with the Tina stating that it would require specific steps to open. The only way for the lock to be open would be if someone knows how it worked. The adventurers then come it to be highly possible that Tsuibayaya intentional moved to the village chasing the Legend of the Mermaid, and somehow acquired the key to open the gate. They decide to enter and follow the cave, and after traversing through the tunnel finally come out to a beach. There to the surprise of the protagonist the sea is actually freshwater not salty as stated in the books of Ashurbanipal. To cover more ground Blue Roses and the contact team split to search for Tsuibayaya promising to use [Message] to stay in contact.
Just as the group went their separate ways, the protagonist's team is attacked by two Giant Crustaceans. After dealing with the monstrosities, the group discover traces of a camp, presumably belonging to the dwarf. Seeing the blood and multiple crab bodies the adventurers think that Tsuibayaya was killed. Shizu appearing alongside with the rest of the Pleiades, deeming that they were safe from being noticed by Blue Roses, states that its too early tell. While Lupusregina makes a claim that the dwarf may have been sniped and betrayed, Narberal points out a more logical direction. Following the bloodstains the trail leads to a nearby cave. The contact team decide to head there alone to avoid the Pleiades exposure to Blue Roses if the dwarf is found.
The contact team walks through the cave searching for their quarry. During the search Narberal and Soi trade playful jabs at one another which surprises Surako with their camaraderie. The two maids explain that they are like a twin set and that they consider themselves to be the third oldest among their siblings in the Pleiades. Though they haven't decided who is older between the two. The group's chat is disturbed when a voice calls out for help in the darkness. Hurrying they find a dwarf being attacked by more crabs which Narberal uses her magic to fry. After confirming his identity as Tsuibayaya, they attempt to help the injured man, but more crabs come. Blue Roses soon appears to deal with them. Lakyus explains that they heard a scream from the different cave entrance, as it appears there is a network of tunnels interconnecting them. Evileye inquires if the group encountered any weird slimes, which causes Surako be sweat as she think that they are talking about her. Fortunately that does not seem to be the case as the slimes Evileye mentioned were native to the tunnels that Blue Roses encountered. Lakyus then takes over the treatment of Tsuibayaya, healing him with her magic.
After being healed by the priest, Tsuibayaya asks who they are and if the villagers sent them. when Evileye corrects him, stating that they were sent by the Kingdom to pick up the armors he promised, the craftsman realized it was already that time. Tsuibayaya confessed that he did receive a notice but did not read it as he was busy with his own project. Now that he is saved the adventurers hope Tsuibayaya could return with them back to the village so they could claim the armors. Tsuibayaya blunt refusal shocks them as he remains adamant to meet his appointment. When he stays muted on whether or not his intentions are concerning the mystery of the mermaid legend, Lakyus subtly blackmails him to reveal unless she will tell his village that he was in a forbidden area. Tsuibayaya confesses that he is searching for the mermaid in the legend, but not for any historical or ecological reasons but to birth his only goal in life----to make the best swimsuit.
The rest of Blue Roses are clueless of what the craftsman is talking about save for Evileye who has heard of the item in question. To give them an example, the dwarf shows the adventurers his prototypes. While the adamantite adventurers feel that the garments are a bit too exposing, they note that the material is of high quality. The contact team of Nazarick take note of the items and see that they are similar to the swimsuits they utilize. The dwarf then explains that ever since he heard about swimsuits he became fascinated by their beauty. So in order to complete his ideal swimsuit he left his native Azerlisia Mountains to go on a journey. He decided to set up shop near the sea to create water resistant materials, and tried using various materials like fish scales, skin, liver and fat. In order to support his work and living expenses, he began to deliver armor to the Kingdom. Tsuibayaya came to realize that the best material for his swimsuits were the scales of a mermaid. The adventurers find the existence of a mermaid to e far fetched but the dwarf believes that it is real and vital to his work. Despite the threat of Chaos Beasts, the dwarf stated that he did not care about the Kingdom and everything was for the sake of his research. He even stated that all his altrustic work in the village and being good friends to the chief was for him to gain their trust to get access to the beach to find the Legendary Mermaid so he may get his materials.
The protagonist gets his confirmation that Tsuibayaya isn't a player, however continues to listen to what the dwarf says. Soi wonders why the dwarf didn't remain in his homeland to do his research, which Tsuibayaya answers that he swimsuits cannot be used in mountains. He learned of the existence of swimsuits from the oral histories of his people from being known the Boastful Sage. The Boastful Sage was a traveler that existed around two hundred years who proposed many various magical items, sadly he could not explain the mechanism of how they worked or how to make them. But his ideas were slowly accepted by various people who developed means to recreate his ideas and can be found in the markets of today. The swimsuit is apparently one of this sage's ideas.
While Blue Roses now understands Tsuibayaya's reasons, she still wishes him to return to the village so her team can get the armors, stressing the point that many soldiers are fighting various threats and need his equipment. Tsuibayaya then offers an idea, and asks Blue Roses to fine the Legendary Mermaid for him in exchange for the armors. Gagaran is not amused by the dwarf, but is stopped by Lakyus who demands the dwarf to explain. The dwarf tells them that he has dedicated his whole life to making swimsuits, and the time to meet this Legendary Mermaid is running out. Evileye notes that convincing the dwarf to change his mind would be difficult especially given how stubborn Tsuibayaya is. With no recourse Lakyus decides to cooperate and asks the protagonist for help.
Since Tsuibayaya is considered to be unaffiliated with any players, the protagonist decides to lend their aid as they wish to check Tsuibayaya's workshop and find any traces of strong existences. Gagaran is still furious at being used by the dwarf so she decides to relieve her anger on a bunch of hungry crabs.
Regrouping at the beach Tsuibayaya gives the adventurers the full Legend of the Mermaid. From its contents the dwarf explains that when four stars in the sky appear it signals the time for when to meet the mermaid when water returns to the sky, where many pools exist leading to the abyss where water is separated. To call forth the mermaid a Promise Stone need to be cast into the pool when the stone resonates. Once it tossed into the water the mermaid will come, and according to legend will return her love and empower them.
From the legend, they deduce that the stars mentioned can only be see during this time of year. The water returning to the sky may also mean that the meeting is when water evaporates, and a clue that the time limit of the site and that it will vanish when all the water leaves. Tsuibayaya gives them a piece of a fragment of a Promise Stone which will help the adventurers in locating a more complete one. The protagonist and their allies then state that they would handle locating the site of the meeting. While Blue Roses then agrees to take charge in finding the Promise Stone on the beach. Tsuibayaya decides then to give his prototype swimsuits to Blue Roses in the meantime as they will be more effective in his gear when fighting against aquatic monsters. Lakyus seeing the logic behind his words, agrees and accepts the equipment, though suspects that the dwarf just wanted an excuse to see the women in swimsuits. The contact party from Nazarick, decline stating that they have their own gear. When the dwarf offers to help Blue Roses in the equipment, his help is flatly rejected. Among Blue Roses Gagaran sees that she is without a swimsuit, which the dwarf states that he has none to give her. Tsuibayaya decides that he will return back home to prepare his swimsuit which Evileye then using her magic to fly back with him to the village.
The protagonist then takes the opportunity to report to Momonga on the mission's development. While the origin of the swimsuits turn out to be unexpected, Momonga sees that this "Boastful Sage" who is responsible for various magic items two hundred years needs to be investigated. Still the news of the Legendary Mermaid piques Momonga's interest and gives permission for the Pleiades to use their swimsuits on this mission.
Once Blue Roses is gone, the rest of the Pleiades reunite with the contact team and don their swimwear. They decide to search for the place where there are a "lot of hidden holes in the water," in a place where the "water is divided." Based on the legend the group assume that the "hidden holes" refers to an underwater cave system, and that the "water is divided" means it literally. Yuri then has her sisters, Lupusrepgina, Shizu, and Entoma separate from the protagonist's party to conduct their own investigation. They come to what appears to be a cove along the coastline, yet the cove is closed by a sandbar and it seems that the water level rises and connects to the ocean when the tide rises. Thus a big pool of water separated a few feet from the sea is where "water is divided". As Yuri investigate the pool, she slips and falls in. Her sister Shizu attempts to dive in after her to save her only to realize her flotation device prevents her from fully submerging. It is not necessary as Yuri resurfaces reporting to the maids that she found the abyss in the legend and tells them to inform the protagonist.
Back to Blue Roses, Evileye returns now in her own swimsuit that she received from the dwarf craftsman. So far Blue Roses doesn't have much success in locating the so-called Promise Stone. All they have done so far is collect stones along the beach but the problem is that they do not know which one even with the fragment they have as reference. Lakyus has been fuming over the problem whilst the other girls bored from the search are taking a break in the sun and water. Evileye feels that though the dwarf has a bad personality she hates to admit that he does excellent work in clothing. When asked why she wore a swimsuit in the first place, the magic caster claims that she was pressured. Tina though thinks that the reason why she was resistant to wear a swimsuit is because she lacks a chest to show off earning her Evileye's ire. Gagaran still feels left out from being unable to wear of swimsuit of her own. Though as therapy takes to killing crabs to divert her mind. Before the women can continue a whistling noise is heard. Lakyus who has been pondering over the legend and the Promise Stone, reveals that the said object actually bears a weak magical signature and that it can retain it so long as mana is poured into it creating the resonance. As proof she demonstrates by channeling her magic into the fragment causing it to glow and create the sound. The adventurers see now that they need a whole Promise Stone to summon the Legendary Mermaid when they toss the stone into the abyss. Evileye then brings up the cave in which the explored when they found Tsuibayaya remembering that the slimes they faced had absorbed large quantities of magic. This in mind, she believes that they can acquire an intact Promise Stone from one of the slimes there. The group then head to the cave, where initially finding a lone slime soon turns out to be a whole colony. Once the slimes are wiped out the group finally acquire the Promise Stone and hurry to rendezvous with the protagonist and his allies eager to see for themselves if the mermaid in the legend is true.
Once learning that the protagonist has already discovered the place to meet the mermaid, Blue Roses arrived with the Promise Stone. There they see the protagonist, Surako, Soi, and Narberal. The latter two having replaced their swimsuits with normal gear greet their colleagues and direct them to the pool where they are to summon the Legendary Mermaid. They explain that there are a lot of underwater caves in the pool and deduce that the Promise Stone emits a sound underwater to call the entity. To determine whether its true or not, Lakyus then pours her mana into the stone and tosses it into the pool. After an anticlimactic start the Legendary Mermaid soon surfaces, but to the surprise of the adventurers the "mermaid" is actually a male merman. The merman is equally surprised that the adventurers had summoned him as he was expecting someone else to call him and even more perplexed that they only want his scales rather than his power. All is explained when the merman states that he was once a warrior that fought alongside humans and had fallen in love with a human princess. However due to the divide in species they had to part and the merman chose to exile himself to the seabed along the cost for untold years. While giving a few of his scales is trivial, the merman longing for a battle offers to give them his scales unless they defeat him. Gagaran immediately accepts the challenge much to her friends dismay. The first round of the fight though is lacking as the merman is weaker compared to the adventurers on land. The remaining Pleiades observing the battle see that no help is necessary and decide to continuing monitoring the situation.
However the Legendary Mermaid then changes the battle field but call the tide and pushing the advantage to him. The adventurers find themselves outmatched and outmaneuvered by the merman in his element. It took the intervention of Shizu who aimed a sniper round at the merman that allowed for Gagaran to land a blow and defeat the demi-human. The attack that earned the adventurers their victory was attributed to Soi, claiming it to be one of her assassin skills to maintain Nazarick's cover. The merman though beaten, admits his defeat and then offers his scales to Gagaran, pleased with the encounter as she reminded him of his lost love. That being said the warrior then retreated back to the depths.
The adventurers having returned with the scales from the Legendary Mermaid, presented them to the dwarf craftsman. The dwarf upon receiving the item for his perfect swimsuit immediately took to his workshop. The adventurers eager to get on with their business had to sit through the drama played out by the dwarf and his presentation of his masterpiece. Once he finished making the swimsuit, which was more revealing than his prototypes, he insisted that it be worn by one of the adventurers. Ignoring their pleas for the armors, he selected Gagaran to wear his item, the Sage's Swimsuit, deeming her with the best body for his work. Gagaran who had been initially hurt at being left out from trying a swimsuit decides to go along with it. Though while her companions question the dwarf's aesthetic tastes on "beauty" they watch Gagaran fulfill the request.
The sight of Gagaran wearing such a skimpy merman scaled swimsuit brings mixed results to the adventurers who view it as distasteful. In contrast, Tsuibayaya believes that the muscled bound woman perfectly accentuates his work. Believing his work to be perfect and that he had finally created the best swimsuit the dwarf formally gives the item to the adventurer without any regrets, in gratitude for allowing him to see his achievement.
Later at the gates of the village he, alongside the protagonist and Surako, see Blue Roses off as they escort the armors to the Kingdom. Surako noticing that Tsuibayaya has been silent, asks what is troubling him. The craftsman confesses that after spending so much time and effort in creating his ideal swimsuit, he now finds himself at a loss of what to do now that he accomplished it. The protagonist seeing that the dwarf's passion to create swimsuit was genuine, decides to show the dwarf a secret. On cue the homunculus directs Tsuibayaya to the assembled Pleiades, who fully reveal themselves in their swimwear. Tsuibayaya is speechless of what he sees, but recognizes that the women are wearing swimsuits in better quality than his own ultimate product. The swimsuits make him realize that his work is not complete yet and that it has only begun. He then begs the protagonist to be allowed to study these swimsuits for his work.
Back in Re-Estize, Lakyus is praised by Princess Renner for her part in retrieving the armors. While the leader of Blue Roses believes most of the thanks goes to the protagonist and his allies, the armors have proven to be truly an asset as now the soldiers in the Kingdom will have higher morale thanks to the superior equipment. Lakyus still has mixed feelings about the dwarf back at the seaside village as his selfish desires are what led to the production of the high-quality armors sought by the royal family. Her thoughts drift back to the protagonist and Narberal, wondering if they ever got to receive armor from the dwarf. However she brushes her concerns aside, believing that the mission was a success since Gagaran is happy at her newest acquisition from the little adventure.
Meanwhile in Nazarick, Demiurge states that sending their agents to the seaside village was a stroke of genius on Momonga's part as now they reinforced their relationship with the higher-ups of the Kingdom thanks to their aid. Though Momonga knows it was purely coincidental he accepts the praise from both him and Albedo, but directs the success of this mission to the real heroes, the protagonist, Slimeko and the Pleiades. Momonga questions the group on the status of the Legendary Mermaid, which he is informed by Solution is being monitored by summons. The merman being a strong existence may be harmless now as certain measures are being taken to dispose of him if he becomes a threat. Momonga though believes that it would be a waste to kill a being of such caliber and decides to patiently wait for the right time. The more concerning news is the existence of the Boastful Sage, who is definitely an existence similar to Momonga. While the Overlord is unsure if the entity is just a special case or if he may be the cause of Nazarick's collapse he orders his subjects to gather as much information on this Boastful Sage as possible.
All that remains is what to do about the dwarf. Understanding that the dwarf wishes to study the swimsuits he has under its possession, Momonga gives permission to allow the craftsman to research the items. It is Momonga's belief that through a combination of items from YGGDRASIL and the knowledge of the New World, it would be possible to reach higher levels of crafting. Thus the new strengthen equipment would help compensate for various individuals suffering from level loss. By giving the dwarf a real article of his study, Nazarick would reap the benefits of the exchange. After the deal was agreed upon, prototypes of swimsuits were regularly brought to Nazarick as research material and offered to any who would like to try them.