a kin is a character (or characters, you can have more than one kin) you associate/identify with. kins are to help you express yourself, comfort you etc.

When some little bitchboy is acting like a little tiny pee pee poo poo baby and messing up the group plans.

A large community generally centered around "relating" to a character one way or another, also the act of doing so. Essentially, after looking at a character and identifying with or as them, the definitions split.
1. Coping; many people kin characters to cope with their situation or illness.
2. Reincarnation; others believe in the Multiverse Theory and when someone dies, their soul may hop between universes.
3. Just for fun; kinning isn't that serious, so some may identify with characters for the fun of it.

1.) Shortened way of saying otherkin

2.) Liking or relating to a (usually fictional) character so much that one integrates thr character's behavior, style, and (in some cases) physical features. Often seen in role-playing communities and on tumblr

Liking or relating to someone so much, it's like you're literally them/another way of saying "same" or "me" Related to otherkin

A shorter version of kinfolk; meaning one's family. Someone who is connected to you by blood or marriage, i.e. your kinsman, kinswoman, kindred, relation, relative.

close friend or brother