Possessed by Mahiru

Possessed by Mahiru is the eighteenth chapter of the Owari no Seraph manga.

Short Summary
Yū chats with Shinoa, and he convinces her to save Mika with him in the future. Guren arrives and, in order to teach Yu about is weapon, Shinoa manifests Shikama Dōji. Guren orders his weapon, Mahiru, to possess him and easily knocks Yū off the roof top. Afterwards, Shinoa and Guren discuss Mahiru Hīragi.

When the rest of Shinoa's squad arrives, Guren orders Shinoa and Mitsuba to teach them how to activate their weapons. Yū returns alive and asks Guren about the Hyakuya sect, as well as wanting to know if Guren would want to take in Mika as well, saying that he will do whatever Guren wants so long as he can get Mika back. Guren answers that everyone there is family, and family works together to bring family back.

Long Summary
In Shinjuku, Tokyo, Shinoa joins Yū on a rooftop. He explains he is looking west because he believes Mika is there in Sanguinem, which is the vampire capital located somewhere beneath Kyoto. He swears that he will get Mika back, and he convinces Shinoa to help him. He holds Shinoa's hand for a moment, making her blush and feel flustered although he does not react to the physical contact at all.

Guren arrives, claiming that both Mitsuba and Shinoa can teach them how to use their weapons properly. Shinoa manifests Shikama Dōji and explains that manifested demons can use special abilities. The other type of demon possesses the user to grant immense physical strength. Yū and Guren spar until Guren orders Mahiru to possess him and promptly flings Yū from the rooftop.

After hearing Guren summon his demon by calling out her sister's name, Shinoa holds her scythe at Guren's neck. She reveals that her weapon specializes in long-range combat and consequently stands no chance against a melee fighter like Guren at that range. Guren calmly says he would let Shinoa kill him. Shinoa asks him if that is his way to atone for killing her sister, Mahiru. She says Mahiru became a demon after completing the method for making Cursed Gear and saving the world. Even though that all Mahiru wanted was to love Guren, she became consumed by her research.

The two discuss the events of eight years ago, when the world ended. The Apocalypse Virus killed any adult who was not fortunate enough to receive a vaccine against it. The Four Horsemen of John killed the survivors. Concerned for their dwindling food supply, vampires took over as many cities as they could. That event is now referred to as Armageddon, and people believe it was divine wrath against humanity for the sins of overpopulation and over-indulgence.

Shinoa explains that she was not close with her sister because Hīragis are raised without knowing familial love. Shinoa asks Guren if Mahiru is commanding him from within, and she asks him to stop what he is doing if his goal does not benefit Yu. Guren asks her what has gotten into her. She explains that Yu was the first person who ever told her he needed her, and she wants to live up to that.

Yū returns, and Yoichi, Mitsuba, and Kimizuki arrive as well. Mitsuba says they have more than half an hour left until their scheduled meeting time, but Shinoa says that was completely different than what she and Yu were told.

Guren tells Shinoa that Mahiru is dead, and he is in control. He says Shinoa and Mitsuba can teach the others how to use their weapons.

Yū asks Guren about the Hyakuya Sect and about the orphans being used as guinea pigs. He asks if Guren rescued him in order to use him. Guren answers that he has no time or resources to rescue those he cannot use. Yū wants to know if he needs Yū and if he would want Mika as well. He says he will do whatever Guren wants as long as he can get Mika back. Guren says that everyone standing there is family, and family works together to bring family back.