Mika and Yu are finally reunited with each other. Yu is shocked to learn that Mika is alive and is now a vampire. Yu tells his friends that Mika is his family and stops them from attacking.
With the arrival of vampire reinforcements, Ferid decides to kill every human except for Yu, with the intention of turning him into a vampire. Mika warns him and proceeds to get Yu out of the situation. Yu gets confused on the turn of events, as he asks Mika what is going on, he sees his friends incapacitated by the vampires. Outraged, Yu suddenly went berserk and transformed into a mysterious being that wants to "punish all sinners."
Guren hits Yu, yelling at him and asking him why he didn't kill the vampire when he had the chance. Guren begins hacking up blood. Shinoa's squad also asks Yu about what just happened. He identifies that powerful, childish, and arrogant vampire as Mika, his family. Naturally, the humans are shocked.
Ferid says that those humans are obviously using Yu, and Mika claims he will save Yu from the ugly, greedy humans. Ferid says a human could never be one of them, but he volunteers to turn Yu into a vampire. Mika responds by threatening to kill Ferid if he so much as lays a single hand on Yu. Ferid claims he was joking and offers to keep the other humans busy while Mika rescues his "beloved princess."
Yu shouts, asking if Mika is really Mika. Mika does not answer, but Yu is so happy that he cries. Ferid blushes and calls it an "utterly adorable reaction" before drawing his sword and preparing to slaughter every single one of the other humans present.
Then, Thirteenth Progenitor Crowley Eusford arrives. Ferid slides his sword back into his scabbard and decides to turn the human soldiers into livestock instead of killing them.
Guren curses and orders a retreat. Ferid plays with Yu and Guren right up until he lays a hand on Yu, which causes Mika to immediately cut off the offending limb. Catching his arm, Ferid claims that he was just joking.
Mika approaches Yu, asking him to forget those on the battlefield and run away with him. Carrying Yu bridal style, Mika makes some distance until Yu pushes himself out of Mika's arms. Mika claims that Yu is in a bad place, and the humans are using him. Yu says that Mika sounds like he is no longer human, and Yu finally realizes that Mika was turned into a vampire. Yu asks if it was his fault for running away, but Mika tells him it was not. Mika claims he is Yu's only true friend and pleads with Yu to go with him. As Shinoa screams, Yu looks back at his fallen comrades.
Suddenly, Yu screams. His left eye becomes dark and appears to bleed.
Inside his mind, Yu asks Asuramaru what is going on. The demon denies attempting to take over his body, but he calls Yu a monster and says that Mika is right. Asuramaru recommends going with Mika and running as far from the humans as he can before all of Yu's humanity is lost. Unfortunately, time has already run out.
Black shapes sprout from Yu's back while he screams, eventually forming into a single wing-like construction from the upper left quadrant of his back. Mika asks Yu to stop, but Yu swings his sword at him. Yu then raises his sword and swings it toward Crowley, decimating a block of the damaged city and leaving a crater in his wake.
Ferid asks Guren about that monster. In the meantime, Yu mutters that sinners must die, and he must kill all sinners. Yu approaches Shinoa with murderous intent.
List of characters in order of appearance:
Manga panels provide a visual overview of the events of Chapter 13 with depictions of the characters, Seraph of the End world and scenarios.