Back in my college days, I got involved in a collectable card game called Legend of the Five Rings, a game partly inspired by Musashi's Book of Five Rings. It started with 8 factions or "clans". The second time I actually played the game, was in a local draft tournament I was dragged into, and got handed a Crab Clan (a faction deck). I lost horribly but learned the Crab faction was an extremely strong defensive military faction (there being 3 different ways to win the game - military, honor/dishonor, enlightenment). Anyways, I stuck with the game and the Crab faction for several years in college.
The Crab clan is divided into 4 "families", the Hida (the main family, the one from which the leader of the clan comes, known for its strength and direct military prowress), the Kaiu (engineers, siege specialists, tacticians), the Kuni (spellcasters specialized in fighting demons), the Yasuki (merchants who keep money and weapons flowing to the Crab war machine), and the Hiruma (military scouts and stealthy hunters, known for stamina, speed, and quick wits).
At about that time I was starting to have an online presence (i.e. college in '97) and started using the Hiruma family name as part of my usernames, as I liked their characters.
Kai comes from a certain famous mechwarrior whose books I read when I was even younger than that, and who (at least early in his career) tended to lose his mech, but generally won battles single handed at ridiculous odds.
I should point out Hiruma is the family name of the handle, so in English you might read it as Kai Hiruma.