Cursed Guinea Pig

Cursed Guinea Pig is the seventeenth chapter of the Seraph of the End: Vampire Reign manga series, written by Takaya Kagami and illustrated Yamato Yamamoto.

Short Summary
Kureto Hīragi challenges Yu to a fight of swordsmanship alone, but Kureto activates his demon without hesitation. Kureto approves of Yu following orders without question, but Yu attempts to strike him once his back is turned. Shinya defeats Yu easily as well because Yu does not know how to properly use cursed gear. Kureto is searching for a vampire spy.

Kureto brings in a bound Yoichi and Kimizuki. He asks about Yu's history while having them stabbed. He tells Yu about the Hyakuya sect. He offers to turn Yu into his subordinate, which Yu turns down. Kureto then says he would have killed Yu if he had accepted.

Finally leaving the meeting, Yu demands an explanation from Guren.

Long Summary
Guren meets with Mahiru in his mind while Shinoa and Mitsuba chat. Mitsuba said she was promoted to a "Vampire Extermination Unit Second Lieutenant." Despite being a Hīragi, Shinoa says she will never be promoted because her elder sister, Mahiru Hīragi, betrayed the family a few years ago. Mahiru was such a genius that their father never bothered to even meet Shinoa, since Mahiru was the brightest candidate for heir of the family. This caused Shinoa to be discarded and regarded as unimportant, which she says means she does not have to challenge Kureto and has no need to fight her siblings for power.

Shinoa asks Mitsuba what information she gave them in order to receive that promotion. Mitsuba denies giving them any information. She said they did not know about Yu going berserk, which Shinoa uses to infer that Yu is not part of an official Demon Army experiment.

Shinoa accuses Mitsuba of having a crush on Yu, which she vehemently denies.

In the First Office, Kureto orders Yu to show him his swordsmanship without activating his demon curse. Shinya warns Yu against trusting Kureto. Kureto orders his demon, Raimeiki, to possess him, effectively activating his gear at an advanced level. Yu calls him out on cheating, but he has a sword at his neck before he gets far. Yū complains that was not fair, but Kureto says the battlefield is not fair. He says he approves of Yu obeying his superior's orders without question and states that it is hard to believe Yu is a subordinate of Guren--until Yu attacks Kureto from behind while he is talking, and Kureto's aide (Aoi) blocks the attack, saving Kureto. He takes back his words and states that Yu is definitely Guren's subordinate.

Kureto orders Major General Shinya to attack Yu next, and it is revealed that Shinya was adopted by the Hīragi family. Shinya fires Byakkomaru at Yu, leaving Yu confused when nothing happens. Manifested tigers appear from Yu's left, and he strikes at them. This leaves him open, and Shinya puts his sword at Yu's neck. Shinya informs Yu that Byakkomaru is a long-range weapon, so he would stand no chance against powerful melee-range fighters. He tells Yu that he has not learned about demon "manifestation" or "possession" yet, so this was the most that could be expected of him.

Although Shinya declines to give his name, Kureto provides it, saying that Shinya was originally from a junior branch family and was despised for it. He said that if Yū wanted to kill Shinya, no one would care.

It turns out that this interview was largely to fish out a vampire spy hiding in their ranks, and Kureto was testing both Shinya and Yu. Kureto snaps his fingers, and a pair of soldiers drag Yoichi and Kimizuki into the room. Both boys have been disarmed, bound, and gagged. Kureto says he will kill them if Yu resists. He says Yu is a rare talent who qualified for a Black Demon series weapon in a short time. Although this is also true for Yoichi and Kimizuki, Yu is the only one who did not have a thorough background check done first. He asks Yu about his origin and mission. When Yu is confused and denies knowing what he was talking about, a soldier stabs Kimizuki through the left shoulder. Kureto orders Yu to tell him the truth, then orders Yoichi to be stabbed as well. Yu says he will tell them everything he knows, and Kureto simply says that no one goes against the wishes of the Hīragi family.

After going over Yu's past, Kureto asks him if he is a survivor of the Hyakuya Sect, which was once the most powerful group of spellcasters in Japan. Confused, Yu answers that it was just the name of the orphanage he grew up in. Kureto explains that the Hyakuya sect was an organization that used orphanages to collected orphaned children for numerous insane human experiments. He states that Yu and his family were probably just a batch of Hyakuya guinea pigs. He says Guren is trying to manipulate whatever experimentation the Hyakuya did to Yu for his own purposes.

Kureto asks Yu to become his subordinate, but Yu says he does not care and asks for Yoichi and Kimizuki to be released. Yu says that Guren would never stoop this low, and Kureto states that is why Guren will never catch up to him. Kureto says that if Yu had stepped forward to become his subordinate, Kureto would have killed him. Kureto releases the three soldiers.

The three boys meet Guren, Shinoa, and Mitsuba. Yu demands that Guren both explain what happened and teach him how to use his cursed gear properly.