I'll write some imagines/drabbles based on these headcannons in separate chapters.

Headcannon#1: Kariya is actually good at different skills for he used to belong in a wealthy family that forced him to learn a lot of things. And since he is one of the oldest child at the orphanage, he has to take care of the younger kids.

Headcannon#2: He is a talented baker because it was his bonding activity with his mother before she died.

Headcannon#3: He constantly keeps on sneaking out of the Sun Garden during the first year of his stay causing him to know random people.

Headcannon#4: He's the cuddly type when sleeping.

Headcannon#5: He might get hurt and hurt other people when they say something bad to him but his anger is too much when you do those things to the people he cares about.

Headcannon#6: The type to ignore his feelings to make someone happy (even when he looks like he's not).

Headcannon#7: Very talented in playing the violin because it was the very first instrument he played and he was personally taught by his father.

Headcannon#8: Surprisingly close with Yukimura, Taiyou, Shuu and Hakuryuu.

Headcannon#9: He started playing pranks because of his father.

Headcannon#10: He knows that the adults from Sun Garden are actually the so-called aliens that invaded ten years ago and yeah... He doesn't care.

Headcannon#11: He accidentally saw Reina's cross dressing hell and was then soon forced to join.

Headcannon#12: He keeps on getting forced to crossdress and act like a girl that his thoughts change from 'No fucking way! I don't want to do this!' to 'Again? Oh my god why again?' and lastly 'Let's just get this over with'. He's terrified about the fact that he's getting used to it.

Headcannon#13: Not the type to easily trust people. It took months for him to trust the people at the Sun Garden. This is also the reason why he wasn't quite comfortable when Tenma and the others trusted him so easily.

Headcannon#14: Because of his inability to easily trust people, he's the type to easily suspect something and observe things to prove it.

Headcannon#15: He actually suspected Shuu to not be human.

Headcannon#16: Is the easily embarrassed type. He blushes so much and hides his face with his hands. Also curls up into a ball and if with a blanket, he uses it as a cover. If not, he'll lock himself up in a room or space.

Headcannon#17: That type of reaction (HC#16) happens when he is caught in surprise. He'll only blush hard, he won't hide, if it's something that he suspected to happen. But if it's a surprise, then HC#16 will happen.

Headcannon#18: A person that can easily know if someone is in love even if they don't show it but he's completely oblivious if it is directed to him. He'll only know if one makes an effort to say and show it to him.

Headcannon#19: Everyone agreed that his best crossdressing clothes are the maid outfit, school uniform, and formal dresses.

Headcannon#20: He's a human cat. A. Human. Cat.

Headcannon#21: There are people that are attracted to him but are not sure if it's 'love' (*ahem, ahem* Kirino, Shindou, Hakuryuu, Tsurugi, etc. *ahem,ahem*). There are also people that are pretty much head-over-heels in love with him. (*ahem,ahem* Taiyou, Shuu, Yukimura, Tenma, etc. *ahem,ahem*)

Headcannon#22: The child who have met all of Legendary Inazuma Japan and Raimon 11.

Headcannon#23: Tutoring his friends is his job along with Taiyou and Tsurugi.

Headcannon#24: There was one time where he went out while crossdressing and he was almost harassed. Good thing, Nagumo and Suzuno came to save him. It scared him and ever since that day, the 'aliens' decided that whenever he goes outside while crossdressing, there MUST always be someone else with him.

Headcannon#25: He appreciates it but " Can you guys stop your over protectiveness?" to the adults of Sun Garden.

Headcannon#26: The only people that calm him fast enough when he's super annoyed, angry or upset are Suzuno and Shuu. Other people can calm him down but not as fast and effective as the two.

Headcannon#27: Suzuno makes Kariya lay down on his lap and the older will just read a book as he strokes the defender's hair. This pleasant and silence filled atmosphere calms him down enough.

Headcannon#28: Shuu drags Kariya out for some fresh air (at a place with a wonderful scenery or somewhere surrounded with nature.) The two will only appreciate the scenery with a warm and peaceful air around them that makes Kariya cool down.

Headcannon#29: His body is quite sensitive, especially his ears, neck and upper thighs.

Headcannon#30: He gained his bad naming skill from his mom.