Aki generally appears to be a very stoic person. But he is actually fairly softhearted. He has a tendency to get attached to others easily, and hates to see people get hurt, especially his close friends. Aki especially has quite close friendships with his teammates/roommates, Denji and Power. The three of them having an almost sibling dynamic, with Aki being the older brother out of it. In battle against Devils (or other) he uses an almost nail like sword, granted to him by the Curse Devil.