Thirteen-year-old Yu attacks soldiers for their swords, but Guren beats him and says he will not be strong enough to receive a real weapon until he has something he wants to protect.
That night, a vampire noble invades Shinjuku, and an evacuation is ordered. Yu runs to the scene to kill the vampire and get revenge but instead chooses to defend a child when the opportunity arises. Guren kills the vampire and grants Yu a sword for choosing to protect someone. He orders Yu to make friends.
Three years later, Yu meets with his squad in Shinjuku prior to a vampire extermination mission.
As he recalls this, he says he will make the bloodsuckers pay. He will find them and will kill them all.
In the present, Yu is thirteen years old. He attacks a group of soldiers with a wooden bokken and demands they give him their weapons. One of them accidentally smacks Yu to the ground.
Yu tells the soldiers they do not need weapons because they do not fight bloodsuckers. Yu says he will make good use of them, so they should give their weapons to him. As one of them warns Yu that he is insulting the entire city guard, Guren knocks Yu hard on the head from behind.
Yu yells at Guren saying it hurt. Guren asks him what problems he is causing this time.
The soldiers realize that this is the leader of the vampire extermination units and the "Hero of Shinjuku," so they quickly try to form up. Guren tells them to not bother and apologizes for the trouble his kid caused. When Yu quickly tries to demand their weapons again, Guren kicks him several feet away.
When the soldiers start to ask if Yu is Guren's child, Guren says he is not actually his kid. He says he found him being held prisoner by vampires, so he decided to nab him. He says now that Yu is such a pain in the ass, he wishes he had not.
Later, Yu wakes up in a room in an apartment complex. Guren is reading a book while sitting at his bedside.
Yu yells at Guren for getting in the way of his revenge and then ignoring him. Guren tells him he is loud and says he does not understand dumb-kid-speak.
Yu shouts that he is a strong warrior now and is doing 10,000 practice swings with his sword every day. He demands that Guren gives him a real weapon, but Guren refuses until Yu is strong enough. He says that anyone who is so dumb that all he can think about is his own personal grudge all day will not be able to protect anyone. He says that being strong is not just about being good with a weapon. Guren says Yu needs something he wants to protect, such as friends, comrades, or family. Otherwise, Yu will be a weakling forever.
Yu says that he does not have any of those anymore and that anybody he even starts to like dies.
When Yu starts crying, Guren asks if he is going to cry and look pitiful just because he did not get his way. Guren calls him a child. Yu quickly wipes his tears and says he is not crying.
Yu says that Guren told him to just think about revenge if he could not find a reason to keep going, and he asks why Guren will not give him the weapons to do that. Guren tells him to quit looking to him for free handouts and says he is not Yu's papa. Guren leaves.
One night, an emergency announcement wakes Yu up. It directs all residents of Shinjuku district six to evacuate because a vampire has infiltrated the city.
Yu takes his bokken and runs against the crowd outside.
He encounters a swashbuckling vampire noble laying waste to the city and drinking human blood. He says he will kill him. As a mother and her daughter flee the carnage, the daughter trips. As the vampire moves to kill her, a pair of soldiers intervene, but the vampire quickly slaughters them.
The vampire approaches the child, stating it has been awhile since he enjoyed a child's blood. Yu thinks that the girl does not matter and decides to get the sword first. After that, he can have revenge for his family and for Mika.
When the girl screams, Yu curses and gets between her and the vampire.
While the vampire is distracted, Guren appears and cuts through his back with his cursed gear. He tells Yu that is the correct answer and to leave everything else to them. His squad arrives with him.
The following morning, Guren says Yu can do it if he actually tries. Guren says Yu decided to save someone rather than try to get revenge. Guren says that, unlike him, Yu is still nice. No matter how hard he tries, he will be unable to live only for revenge.
Guren tosses a sword to Yu. He says he can give Yu a sword if it is not just for revenge. He tells Yu to find some friends and use the sword to keep them safe. Even then, Yu still sees his family being killed whenever he closes his eyes.
Three years later, Yu meets up with the rest of Shinoa Squad in a ruined city and head off to exterminate some vampires.
List of characters in order of appearance: