
Katsumi lost his parents in a strange 'accident' completely inexplicable: he returned home to find them basically disected. This has caused him to show true emotion to pretty much nobody except Sai; and Sai, being the dense fellow he is, doesn't KNOW of the affection, let alone is able to accept it. Katsumi is somewhat morbid at times and can become rather preoccupied with death due to his parents' accident. It was a year before the accident that Katsumi developed his powers as a psionicist and a super hero, and he feels that if he got them trained faster, he might have saved their lives. He cares deeply for his brother, but barely sees him; he knows his brother's boyfriend is Taka and thus Nikki can only see him after school and so doesn't care much when Nikki gets home. Although disturbed by Taka's age in comparison to Nikki, Taka is technically his legal guardian and has always shown a lot of kindness to both boys, so Katsumi puts up with it with only mild feelings of distress. He has no idea that Nikki moonlights as a magical 'girl' or how often he uses visiting Taka as an excuse to do his 'part-time job'.
He and Sai used to go to a school known as 'Ohtori Academy' but left when they started getting 'bad feelings'. Bad feelings are important for psionicists. He's currently undergoing massive guilt he couldn't save Sai's hand.