Despite his young age, Ken is very intelligent and mature. It is shown that this is a coping mechanism due to the death of his mother at a young age, which more-or-less forced him to give up his childhood.  Besides being mature, Ken also knows several words that boys his age don't usually know, such as "bastard," which he usually uses when referring to Strega. Additionally, he doesn't take kindly to when others underestimate or degrade him due to his age or the fact that he is in elementary school. He is very polite to others, and never misses a chance to show respect where respect is due. He is also honest, diligent, and deeply caring towards his peers, particularly the members of SEES. Ken is shown to like and care a great deal for animals, such as Koromaru.

Although especially idealistic, his tragedy with his mother's death torments him in maintaining his sense of justice and the reason to live it belies for him: at first, he responds with a drive for revenge. Although hesitant towards taking down Shinjiro Aragaki, he would become consumed by hatred without thinking of the consequences, specifically the guilt that he will drown in as warned by Shinjiro himself