“This can't be happening! happening! hapPENING! HA-HA-HA-- This has to be a dream! MEME!”
―Steven Universe, Steven Poops on the Universe[src]
He is an unfriendly, cold young man who is always seen checking his phone for new messages from some unseen girlfriend. His cruelty, from his point of view, is justified and deserved, because he sees the Mistakes as a crew of messes beyond saving... So what's he doing with them, anyway?
He hates dogs, and -- I mean, isn't that enough? What an asshole, right? I mean. He hates dogs!
Kainashi is ruthlessly blunt about his feelings for other people - and those feelings are unanimously negative. It seems he doesn't have a kind word to say about anyone around him, and on the rare occasion that he can tolerate someone, he is silent about it. He must run on some opposite universe-version of that old schoolyard rule, "If you don't have anything nice to say, don't say anything at all".
Furthermore, he takes his own age (almost 20) very seriously and considers himself to be an authority on appropriate adultlike behavior, despite acting nothing like one. One could easily say he has a complex regarding younger teenagers, he feels he has to teach them how to be acceptable (as he finds them largely unacceptable, for being teenagers and acting as teenagers do). As with any person who thinks "I have to teach this person how to be acceptable," Kainashi's "teaching" comes from a place of brutal honesty - that is, unnecessary cruelty, emotionally abusive methods of helping someone realize things about themselves, and an eternal stance of superiority.
Kainashi subscribes to an aggressive, abusive gatekeeping school of thought in nearly all things. He instinctively questions and criticizes any teenager who thinks they belong in the LGBT+ community, he instinctively invalidates anyone, period, who thinks they may have a mental illness or developmental disorder that they haven't been diagnosed with - he is hypercritical of teenagers, more than anyone else, thinking that the way to guide them to better themselves and develop is through harshness.
He is critical and opinionated about more things than one would associate with someone always glued to his phone. Kainashi seems to be very intuitive about the true feelings and thoughts of others, but it seems that intuition is always run through a bad filter, so he always sees the absolute worst in people no matter what they do.
And... That's it, as far as anyone can see. He's not a very deep person, is he? What else can I say about him...?
... Well, he doesn't like being touched without any warning beforehand, but, I mean, he's just a touchy asshole, so no news there.
Sabitsuki died of her mysterious illness, "Rust", when Kainashi was very young. His memories of her are scarce and unpleasant - he remembers her as a cold, insensitive mother who made fun of him far too much as a child. Sabitsuki herself struggled with showing affection to those around her due to her innate hatred and distrust of people, but she tried her very hardest for her son. All this considered, you may get him to admit that he misses her if he's feeling sensitive enough.
Ritsu Namine Edit
Kainashi isn't sure what to think of his father. For some reason, "terror" is the first emotion that comes to mind. What is that all about...?
Kainashi seems to despise just about everyone in the Mistakes, and he has no reservations about letting them know. It's just a bit strange, though, why does he stick around with them if he hates them so much?
When seeing Rowan for the first time, Kainashi... How do I say this... He felt something deep and passionate, almost too deep and passionate not to be afraid of. Obviously, that emotion Kainashi felt was blind rage and loathing. He struggles to comprehend that someone could be as cowardly, unintelligent and pathetic as Rowan Inspector-Matthews. In his mind, Rowan is the amalgamation of everything he hates about the Mistakes... Well. Kind of. I think?
Inochitori is the one member of the Mistakes that Kainashi doesn't want to strangle to death and back. They text back and forth quite a bit, joking about the shenanigans they have to witness just by virtue of being part of the gang. Kainashi and Inochitori have more than a handful of emoji-saturated inside jokes regarding their friends.
Kainashi's main fetter is the second-stage Snowbelle, The Machine. Also appearing are the first-stage Snowbelle, The Toy, and the third-stage Snowbelle, The Craftsman.
He also has an alternate universe third-stage, Snowbelle, The ???.