Fall of Ro-Lente Castle

Fall of Ro-Lente Castle was the besieging on the Royal Palace of the Re-Estize Kingdom by the Sorcerer Kingdom's forces amidst the war between the two nations. It also saw the assassination of King Ramposa III as well as the defection of Princess Renner to the Sorcerer Kingdom.

Background
Following the Sorcerer Kingdom's siege on the Royal Capital of the Re-Estize Kingdom, all that remained unconquered was the Royal Palace, Ro-Lente Castle. Inside were the last remaining members of the royal family, King Ramposa III and Princess Renner, protected by their knights, who were preparing to make their last stand.

With the Kingdom's defeat all but guaranteed, Princess Renner seemed to be planning to commit double suicide with her father to evade capture. In actuality, though, Princess Renner had been a Sorcerer Kingdom spy as early as the Demonic Disturbance and was, in fact, plotting to assassinate her father as a display of fealty towards the Sorcerer King.

In preparation for the assassination, Princess Renner made sure to remove all possible obstacles to her "play." Although it is unknown if she anticipated it, Blue Roses fled once the kingdom's defeat became certain while Brain Unglaus went ahead to make his last stand during the siege. As a result, the only person-of-interest remaining was the Princess' bodyguard, Climb. She thus send him on a mission to hide the crown jewels throughout the capital to prevent the enemy from acquiring them. In reality, though, the bodyguard was actually placing the jewels in pre-determined locations to be retrieved later by the Sorcerer Kingdom.

On the Sorcerer Kingdom's side, there seemed to be little-to-no preparation for the castle siege, with their main invasion commander Cocytus making a straight path towards the palace; instead merely waiting for Princess Renner to give the green light.

Battle
The exact events of the battle are unknown. However, by the time Climb returned from his mission the castle had fallen, with all its inhabitants, except for Princess Renner, having been killed. Curiously, there were no signs of a battle, with Climb not spotting any corpses, blood splatters, or even environmental damages.

The Princess also successfully carried out her assassination plot by stabbing her father in the back with the royal sword, Razor Edge, right in front of Sorcerer King Ainz and his retainers, Albedo, Demiurge, and Cocytus. Thus proving her loyalty and being accepted into Nazarick as an honorary member.

Aftermath
This operation effectively dissolved the Re-Estize Kingdom's central government. Though the Kingdom still had territories remaining that were yet to be subjugated, after the battle the Sorcerer Kingdom spread out its forces to take these as well. Sure enough, without the government's aid, these small independent domains would fall with little-to-no resistance.

The incident also served as the final screening test for Princes Renner's admission into the hierarchy of the Sorcerer Kingdom, where the Sorcerer King's three closest aides; Albedo, Demiurge, and Cocytus and the Sorcerer King himself personally take an open analysis on Renner and her overall capabilities as a potential asset or potential threat against their Kingdom should she join. With Albedo and Demiurge having successfully obtained a full grasp of the Former Princess's personality, intelligence, motivations, and overall abilities, this convinces them that they could handle her without much difficulty.

This operation even acted as the building stage for the Princess' personal plot to manipulate her bodyguard, Climb, into defecting with her. By making it seem like her patricide was done under the influence of Demiurge's [Command Mantra], the guard remained blindly loyal to her. The plan was for Sorcerer King Ainz to just kill Climb, after which he would be [Revived] in Renner's care. However, the monarch decided to go off-script by challenging the bodyguard to a duel, which he accepted. In the end, though, it amounted to the same result: Climb was killed and [Revived], after which Renner manipulated the mentally exhausted boy into getting a [Racial Change] into a Demon with her so they might spend eternity together.

Trivia

 * While Renner's full motives for assassinating her father remain unknown, two possibilities can be drawn:
 * It was a test given to her by the Sorcerer Kingdom.
 * She had become worried about her position after the plan to conquer the Kingdom from within was changed into an all-out invasion.