All headcanon found herein is subject to change or retconning at Sorano's whim. I'll probably keep adding more, since I'm only posting this now because I'm impatient.
- From grades one to six he was shunned by the other kids because they thought he was cursed. To be fair he did practically maim three other kids in an abandoned house and doesn't remember how that happened at all.
- Incidents like that didn't happen again until the end of the 9th grade, well after moving to middle school, so some of that suspicion faded. However by the time it did, he was probably being avoided by most sensible people because he hangs with Akira, who always has goons going after him and stuff.
- Kengo used to cry after he and Akira would get jumped, since he'd get beaten on way more. It's just because he's a crybaby though, he doesn't hold a grudge afterwards.
- Maybe because of the possession incident, Kengo's parents always took the family on vacation somewhere when they had breaks from school, while Kengo was little. It was to protect Kengo from teasing or shunning he might have to deal with if he tried to hang out with other kids over break. They never really left Japan or anything; mostly visited places in the city, but Kengo's favorite place is the beach.
- Kengo's parents are both pretty normal and loving parents; his dad in particular is a bit of a goofball and likes to laugh.
- His parents totally have some sort of wanderlust going on though. When Mayu was old enough to take care of the house and watch Kengo they started taking longer trips. The kids could fend for themselves by then, especially since the fuss over that incident with Kengo had died down a lot by then and he doesn't need protecting. Kengo was probably a little :/ about it at first but well... he gets to visit Akira every day so it's fine if he stays home.
- Although large incidents of possession don't happen between sometime in the first grade and the end of the ninth grade, Kengo and Mayu both continued to experience low level possessions from time to time over those eight years.
- Mayu probably met Master a while before Kengo met Kou. Master provided them with helpful tips and items to deal with the possessions, though most likely Master wasn't aware of the extent of Kengo's abilities/problems, since he only really met Mayu face to face regularly.
- Kengo has lots of small fights with his sister but other than that they generally get along.
- Kengo probably got the idea to take up boxing from some boxing sports-manga. He picked it because it was something more realistic that he could do, though he probably secretly wanted to try to be a ninja at first...
- Kengo likes heat. Hot weather is his favorite! And he likes summer activities and stuff. Moving and sweating and then taking a cool shower is refreshing o/. On summer nights he prefers just a simple electric fan over air conditioning. He doesn't like baking in the sun though.
- There is totally a yaoi manga in Kengo's porn stash. He bought it out of horrible curiosity once and can barely look at it without wanting to die of embarrassment. It is shoved the farthest back behind the shelf where he hides stuff.
- Kengo regularly lies to his family about getting into fights. They can probably see right through him but he can't help it anyway because he doesn't want them to worry.
- Similarly, Kengo has never introduced Kou to his family.
- It was probably some offhand comment that Akira made that started it, but it was Kou's fault Kengo ended up with dyed hair and piercings. Kengo was a complete wuss about the piercings part and whined a lot, though he never actually said he doesn't want them. He's just a wuss.
- The ones to treat Kengo's wounds after a fight are usually himself or Mayu (most often himself since he doesn't like letting people know he gets in trouble a lot), but he's also on decent terms with the school nurse.