Background: Has a very broken family. His father hated him from the day he was born, giving him the name "Yue", a girl's name, in hopes that the name would someday kill him. Due to stress in the family, Katou became addicted to drugs, and the only one in his family who seemed to still care for him was his sister. In order to try to destroy her love for him, he attempted to rape her, but was stopped before he managed to complete his goal. Even after that incident, his sister still loved him because he was her brother.
Basic: A drug-addicted friend of Kira.
Information: Believing Rociel was a drug dealer, Katou accepted one of Rociel's pills, thus becoming Rociel's slave as Ruri had. However, he didn't entirely lose his consciousness because he was so accustomed to taking pills. Setsuna - as Alexiel - in a rage after Kira's "death", attacks Rociel in Katou's body, and Rociel flees the body just in time for Katou to get his chest slashed open by the Nanatsusaya. Alexiel saves Katou's soul from complete corruption by Rociel, and Katou finds himself in Hell, where he later meets up with Setsuna. Katou was on Enra ou's side then, trying to kill Setsuna every chance he got, but the two formed a friendship and in the end Katou died again, ensuring Setsuna's escape from Hell. Uriel gave him another body made of plant-like material, and since it hadn't completely settled he could change his appearance whenever he wished, even making himself look like Setsuna in one instance - he even had the third astral wing, because of the seed he'd eaten from one of Set's wings when Setsuna went to save his mind in Hell. He and Uriel work together to trap Raphael and force him to heal Setsuna's body. Katou is a true friend to them all, and does everything he can to ensure their victory. Katou was nearly sliced in half by Lucifer while standing in for Setsuna, pushing Set out of the way in order to take the blow. His plant body flesh is rotting, and he is taking Kira's betrayal none too well. Katou tells Setsuna that he lives because of the promises he's made, but begins to slowly lose his memories. He dies at Heaven's Door, allowing the rest of the group through the door into Azulith.