Kiseki-o's Box

"Kiseki-o's Box" (鬼箱王のハコ) is the twenty-first chapter of the Seraph of the End: Vampire Reign manga series, written by Takaya Kagami and illustrated by Yamato Yamamoto.

Synopsis
30 hours pass by as Kimizuki struggles against his demon, and the group prepares to eliminate a possessed Kimizuki.

Another illusion engulfs him. An 11-year-old Kimizuki nurses his sister Mirai, who was struck by the same virus as the adults despite being a child. The gang of kids Kimizuki works with insist on killing Mirai by Mirai's request. Within the thrall, Kimizuki thinks of Yu and his passion to save his family. Not wanting to be out-done, Kimizuki breaks free of the illusion and counterattacks. Kiseki-o concedes and lends his power to Kimizuki with the warning that Kimizuki has more darkness buried within and would even betray his friends for the sake of his sister.

Kimizuki wakes up, attacking Yu and challenging him to a duel. Both of them use special powers, which should be impossible for possession-type demons.

Characters
List of characters in order of appearance:
 * Shihō Kimizuki
 * Shinoa Hīragi
 * Yūichirō Hyakuya
 * Mitsuba Sangū
 * Yoichi Saotome
 * Kiseki-Ō
 * Mirai Kimizuki (Illusion)
 * Mikaela Hyakuya (Flashback)

Summary
Kimizuki yells and struggles as he continues fighting his demon, Kiseki-o, beyond the 30-hour mark. The rest of Shinoa's squad holds him down. With the increasing chance of him going berserk and losing control, Shinoa warns Yu to be ready to eliminate him.

A bruised and battered Kimizuki keeps standing against Kiseki-o. Kiseki-o mocks him, saying he refuses to submit to the weak. Stabbing him once more and drinking Kimizuki's blood, Kiseki-o enthrals Shiho in yet another illusion.

An 11-year-old Shiho Kimizuki watches over his sister, Mirai Kimizuki, in a prefectural city four years after Armageddon. Mirai apologizes for getting sick with the illness that was only supposed to affect teenagers and older, and she tells her brother that she understands if he abandons her. She tells him she hears him crying every night. Shiho blames this on a demon's illusion, but Kiseki-o corrects him: these are his own personal memories. He says Shiho wanted to abandon his sister.

Knocking on the door pulls Shiho back to attention. Three boys outside inform him that the food is gone from that area, and they plan to leave the next morning. They ask Shiho to kill Mirai since they cannot afford to cart around an invalid. This is what Mirai asked of them, as she cannot move and hates being a burden. When the other boys decide to kill Mirai in his stead, he locks himself in the apartment with Mirai. As she begs for him to kill her, he yells at her to shut up, and the demon points out that he is sick of all this. Kiseki-o analyzes the truth behind Shiho's feelings.

Shiho suddenly talks about Yu. He says that he hates him and cannot stand him, but he greatly respects Yu's ability to risk his life to rescue a family member he is not even biologically related to. Shiho says that, instead of killing his sister, he will choose to die instead. Why? Because he cannot let Yu show him up.

Shiho breaks free of the illusion, then proceeds to slicing Kiseki-o. Kiseki-o is satisfied with standing down for now, reminding Shiho that he is in no rush, and Shiho has plenty of darkness deep within him. He mentions that Shiho would not even hesitate to betray his so-called friends in order to save his sister. He agrees to lend Shiho his power.

Upon awakening, Kimizuki immediately activates his demon and strikes at Yu. He insists that he is in control, but he wants to settle who is stronger between he and Yu as soon as possible.

Yu uses an ability called "Asura-Kannon," ordering it to fan out. Numerous swords manifest behind him as he charges at Kimizuki. In turn, Kimizuki begins a countdown to "open the devil's coffin." Sensing danger, Yu retreats, saying that was obviously a very nasty technique and he had no desire to be within its striking range.

Mitsuba and Shinoa are shocked that either of them could use a special ability at all. After all, this is supposed to be impossible for possession-type demons. Shinoa jokes that Yoichi already did the impossible by manifesting his demon on his own. She suggests the three boys are Lieutenant Colonel Guren's handpicked secret soldiers and mentions that the detailed reports on their pasts have been removed. Mitsuba is concerned that the power struggle between the military higher-ups is kicking off. Shinoa is also concerned for what is to come.

Gallery
Manga panels provide a visual overview of the events of chapter 21 with depictions of the characters, Seraph of the End world and scenarios.