Gehenna Project

Gehenna Project (ゲヘナ計画) is a re-enactment game event in Mass for the Dead that was released on April 3, 2019 to April 13, 2019.

Background
This is a story you should have seen somewhere--. Behind Sebas's assault on the "Six Arms" hideout to save the kidnapped Tuare, a plan has begun in which the Demiurge has full control. This night, the flames of Gehenna attack the royal capital.

Summary
At Sebas Tian's mansion, the Pleiades, Mare, Demiurge and Shalltear gather to retaliate against Eight Fingers. Sebas, not part of the majority of the plan, follows his own agenda the rescue of Tuare, leaves the room for them to discuss their mission for destroying the criminal underworld. Demiurge has Entoma display a holographic image of an individual that is off-limits to all in the squadron especially Shalltear, due to her bloodlust and habit of playing with her prey. Concluding his plan, Demiurge receives contact from a Shadow Demon that an eighth base has been located, and sends Mare with Entoma to go there. Fearing that Ainz might grow weary of the Floor Guardians should they fail him again, Demiurge finalizes the operation and vows that failure is not an option.

Elsewhere, Hilma wakes up from sleeping and finds her manor encased in shrubbery. Behind her stands Mare, who asks if she is the most important person in the manor. Hilma affirms this, trying to affectionately get answers from Mare; but as Mare is relieved to having found her, Hilma is frightened due to Entoma in a corner eating the twitching arm of one of her dead servants. Mare shatters her leg and drags her away by the hair, leaving Entoma to empty the manor of valuables. As Entoma snacks on the severed arm, Gagaran arrives behind her, asking what she's eating; shocked at the sight, Gagaran readies to fight. While Entoma offers a parley, Gagaran cannot do so as an adventurer. When Gagran shatters the ground, loose debris scuffs Entoma's attire; enraged at the disrespect of something granted to her by the Supreme Beings, Entoma fights seriously. She summons Blade Bug and nearly kills Gagaran, but Tia arrives to save her.

As the Blue Rose duo fight Entoma, they have difficulty with her array of insect-themed magics. Entoma replaces Blade Bug with Whip Millipede and overpowers them until Evileye arrives. Evileye offends Entoma for her appearance and says she's weaker than Evileye, causing the insectoid maid to go into a frenzied attack. Evileye frees Gagaran to heal Tia's wounds, as she battles Entoma. When Entoma unleashes a swarm, Evileye seeing her magic similar to that of a Demon God uses [Vermin Bane] and poisons Entoma. Entoma's face falls off, and her lip bug dies, causing her original voice to assert; causing Gagaran to taunt her, sending Entoma with her true form into a blood lust. Gagaran knocks Entoma away, but the clash between her armor and the amid uniform causes her concern. The trio then uses an onslaught of their strongest attacks and spells to wear Entoma down.

With the maid out of stamina and no more bugs in her arsenal, Tia moves in for the kill. But, the a strange red suited masked man appears to save Entoma. After checking to confirm that the maid was still alive, he then turns his attention on the adventurers, his dark aura causing Evileye to become apprehensive with fear as the maid was nothing compared to this being. The masked man tells Entoma to retreat whilst he took care of the adventurers. Evileye, warns her comrades to flee with the utmost haste, but Jaldabaoth attacks and withstands each of Evileye's magic. Using his [Hellfire Wall], he hits Tia and Gagaran killing them unintentionally, even offering condolences to Evileye. He used the spell based on the standard of Evileye's power but is surprised by the difference in their weakness. Enraged, Evileye attacks but is unable to do any point of damage on the demon. Deciding to fight him, Evileye is stopped when Momon arrives, landing in between her and the masked man, and asks which one of them is his foe. Momon ad Nabe who had been flying in the sky via [Floating Board] had seen the scene from above and decided to intervene. As Momon demands to know who his enemy is, Evileye states her name and rank to identify herself as an ally and requests a team up. Reluctant to ask him because of the difference in power to the masked man, Momon accepts without hesitation. The masked named who introuduces himself as Jaldabaoth, accepts Momon's introduction and by the dialogue, Evileye infers Momon is gathering intelligence on Jaldabaoth. When peaceful resolution cannot be met, the two powerhouses clash, which stirs a heartbeat in Evileye.

As they continue Jaldabaoth uses an aerial attack on Evileye, but Momon steps in to deflect the attack. A small parasite breaches his shoulder plate, but Momon brushes it off as insignificant. Momon takes Evileye- fangirling in his arms- to safety as Jaldabaoth falls back to continue his original objective. The demon warns Momon that should he follow, the demonic flames encircling the sector of the city will be the death of him. When Evileye urges pursuit, Momon argues against it as it would mean fighting seriously against a flying demon with incredible power; which Evileye takes as he is protecting her.

Trivia

 * The scenarios in this game event covers the events from Overlord Volume 06.