Aya visits someone in the hospital. It is a young girl (you wonder who she is). Whilst leaving the hospital, he picks up a yellow ball and looks around for it's owner. It happens to be a blind girl, so Aya holds the ball near the wall so she can touch it easily. The girl cries out in joy as she thinks the person in front of her is her elder brother Juu. Surprised by her outburst, Aya leaves hastily. However, the girl faints before he could leave so he sends her back to her ward.
In her ward, her nurse reveals that she (Yamada Miyu) has lost her parents and she has a brother (Juu) who has been visiting her until lately. As Aya leaves the hospital, a car flashes by him and horrible memories flood his mind. He is reminded of the same car knocking a young girl down (that girl he visited). A man (Takatori Reiji) sitting in the car looks back and gives a sinister smile.
Weiß have received a new mission from Persia (their boss). An organisation has been holding human chess games where men go and fight as pawns of a chess game. Many people have been killed in it. Their target is the mastermind of the organisation, Hikage. The only clue they have is that Hikage talks to the contestants/pawns when they win and also, when he gets excited, a red heart will appear on his forehead. Youji gives it up as there are no women around.
Omi works undercover in the club where the human chess game is held. He witnesses the first round. Both 'pawns' are summoned up to the chess board and they put up a fight for their lives. The man from the white side plays dirty and shoots the man from the black side dead. Before he dies, he softly utters 'Miyu'. Thus, the man from the white side has won and the game continues.
Aya joins the game to be one of the 'pawns'. A woman brings him to the game grounds. She tells him that Hikage thinks highly of him. A few guards walk past them carrying the body of the first 'pawn' who died. The woman says that he had wanted to get the prize money for his sister's medical fees. By instinct, Aya feels he is related to the girl with the yellow ball he saw the other day and asks for his name. It is indeed Yamada Juu, the girl's brother. Omi pretends to walk into the game grounds by mistake and notes down Aya's position on the chessboard.
Omi hacks into the main computer system and devises a plan to make Hikage reveal himself before Aya is summoned onto the chessboard. He creates chaos. A voice booms into the club demanding Hikage to reveal himself. A man standing next to the woman (who had brought Aya into the game grounds) immediately claims himself to be Hikage. Omi tries to shoot him with his crossbow from his hideout but was blocked by the walls. Despite the chaos, the woman demands that the game go on. Aya is summoned up to the chessboard. Omi panics. Without much effort, Aya defeats his opponent. The woman gets excited and chooses the next player to fight him. Aya notices a red heart appearing on her forehead (meaning she is Hikage) and confronts her. Hikage merely presses a button which caused all the tiles of the chessboard to fall, taking Aya with them. Aya clings on and saves himself with Youji's garrote. He proceeds to kill Hikage, but sees Takatori Reiji amongst the crowd and switches his target. Hikage is killed by Omi instead. Aya tries to stop Takatori from leaving but in vain. This leaves Ken and Omi wondering what Aya has against Takatori.
Screencaps
The girl that Aya visits
Yamada Miyu
The 'red heart' on Hikage's forehead
Takatori Reiji and his bodyguard