So Who Is Kai?

Kai Chisaki, also known by his villain name "Overhaul", is a major antagonist in the My Hero Academia franchise.

He is the leader of the Shie Hassaikai, a Yakuza organization comprised of villainous Quirk-users. Following the defeat of All For One, Chisaki believes he is destined to become the next ruler of the criminal underworld and plans to destroy the current Quirk society and return the Yakuza to its former glory.

(By the way superpowers are called "Quirks" in the My Hero universe)

So How Is He Like?

Not very pleasent I can tell you that much

Chisaki is shown to suffer from mysophobia, as he is under the delusion that everybody around him is sick and hates being touched since he is shown constantly scrubbing his arm, in fear of any contamination caught onto him.

Due to a combination of an old theory claiming Quirks derived from rats and his mysophobia, Kai believes that Quirks are a plague on humanity, having infected people with "syndromes" of heroism and villainy. He looks down upon those that use their abilities for either purpose, referring to acts of heroic sacrifice or petty crime as "sicknesses". Kai is highly determined to his ambition of eradicating Quirks, not only due to his phobias but also because such a thing would allow the Yakuza to reclaim the power they once held over society. Kai has no moral compass and an enormous ego, viewing himself as the only person in the world who's enlightened to the "true nature" of Quirks and deserving of the spot as ruler of the underworld after All For One's downfall.
Despite this, Overhaul's values are noted to be paradoxical, particularly his over reliance on his own Quirk, which he happened to name himself after.

As the leader of the Shie Hassaikai, Kai is usually levelheaded, thinks strategically, and can come off as nice at first. Kai possesses polite mannerisms and can be very calm and classy even to people he considers potentially troublesome.If aggravated, however, he may display a powerful and visible killing intent.

As stated before, Kai is very germaphobic and hates anything he perceives as unsanitary, frequently remarking about the unclean appearances of certain people and locations. He refuses to be touched by others or even breathe in the same air as theirs, which is one of the reasons he wears an air-filtering plague doctor mask and forces his subordinates to do the same while around him.

If blood, dirt, or some other unclean substance comes in contact with Kai's person, he will start developing hives and lose his usual composure, becoming increasingly unhinged as a result.

Kai doesn't value humans, viewing people as pawns for their utilitarian value and being willing to experiment on them to accomplish his objectives, going so far as to experimenting on a child. He carries this sentiment even towards the other members of the organization to which he has dedicated himself since childhood, treating them as expendable sacrifices for his well-being and having no qualms about killing them off for the most minor mistakes.
The masks worn by Kai's closest subordinates also remind him of this mindset; he doesn't view them as worthy of sharing the same air as his.

The only person Kai has ever shown genuine concern for is the former boss of the Shie Hassaikai, who rescued him from the streets at a very young age and raised him as a yakuza. Kai, to this day, still feels deeply indebted to his boss for taking him in, being adamant in returning said debt by returning the yakuza to their glory days somehow.
Ironically, despite his sociopathic mindset and inhumane treatment of others, this makes his ideals about family much more personal than any other members of the organization. Aside from this, he has also shown to value Hari Kurono, his childhood friend and right-hand man, having healed his injuries and being the only one of his subordinates he does not treat as disposable. (Couldn't find a gif that wasn't discolored to hell)