Aoba Kuronuma

Aoba Kuronuma (黒沼 青葉 Kuronuma Aoba) is a character introduced in volume 4. He is a 1st year student in Raira Academy, and is Mikado's kouhai, who he refers to as "Mikado-sempai". He is the leader of Blue Squares. He has a bright personality and is always seen smiling, but has a darker side that is actually highly manipulative and cunning. He's described as being akin to "a younger version of Orihara Izaya". He does not appear in the anime.

Background
Aoba's parents are divorced. He changed his original surname, Izumii, to his mother's maiden name, Kuronuma.

Aoba has an older brother, Izumii Ran. When he was in elementary school, Aoba was occasionally abused by Ran who was jealous of Aoba because he received more attention. On one occurrence when Ran had overdid it, Aoba set fire to Ran's room as revenge.

Blue Square
Aoba started Blue Squares when he was in middle school. He ceded its leadership to Ran, who, despite knowing Aoba was using him, accepted the offer as the one and only chance to surpass Aoba.

After Ran's capture, Aoba became the leader of Blue Squares again. He attempted to manipulate Mikado Ryūgamine for his own purposes, but Mikado quickly turned the tables when he stabbed Aoba's hand with a ballpoint pen when they were discussing an agreement. Aoba goes on to state that the deal was signed with the blood from his wound, realizing that Mikado had far from shown his true character.