He is twelve years old, and the protagonist of the story. His "true name" is Loveless. Two years ago, he had an abrupt change of personality and became the opposite of his former self. Before, he was a popular, average grade student; now, he doesn't get along with his classmates, but he gets perfect scores. Along with the personality change, he suffered a loss of all his memories. The cause of these drastic changes is still unknown, although he has regular therapy sessions to determine why.

Ritsuka, on his first day at his new school, meets Soubi Agatsuma for the first time. Soubi confuses him with his sudden intimacy and puzzling claims that he was Seimei's fighter. As Ritsuka discovers, Seimei's impromptu will dictates that Soubi shall "become Ritsuka's" upon his death. Ritsuka deeply admired and idolized Seimei, and to discover later there were many things kept secret came as a great shock. It further poisoned his difficulty in trusting others, particularly Soubi.

Despite his young age and inexperience due to his amnesia, Ritsuka is very intelligent and approaches things with startling maturity. The circumstances of his life encourage his lack of innocence; however, there have been notable incidents that bare his still-strong naivety, particularly in sexual love and dating. Despite this, he still has firm opinions and unrelenting ideas about those subjects. It is these opinions that clash dramatically with adults and authority figures around him, most notably Soubi. Ritsuka is a pacifist, and strongly opposes violence under any circumstance. Soubi has remained fairly silent on the issue; however, he seemingly doesn't object to pain and punishment under certain circumstances.

Love is an uncomfortable subject for Ritsuka. He is wary of compliments, and doesn't like hearing phrases such as "I like you." Early on in the series, Soubi says "I love you" frequently, which Ritsuka doesn't believe is true. Because of Ritsuka's cynical reaction, Soubi stops saying it altogether after volume 2 of the manga. Still, Ritsuka's inner conflict over whether he believes what Soubi says becomes a source of great tension and bitterness in their relationship.