[whsie]

Originally Posted by Richocet

Well with a background like that I only hope more so that this gets approved and translated on BT.

Spoiler for ...why:

why did he quit after that long a time? Is that why he knows the principal??

Spoiler for more background:

I don't remember the details, but from what I remember, he left after the organization was burning down around him. He went and retrieved Rentia and later went into the real world. His background was primarily explored in volume 4 when a fellow assassin who used to call him "brother" returned as part of the evil organization that the current "Ren" is part of.

His past with the principal isn't that closely explored. That principal is actually really, really powerful and one of the few that could potentially be stronger than the old Kamito. She had the position as one of the 10 royal sword dancers (and even among them, the best) in the country until she voluntarily retired. She even taught Kamito some of his ace moves. For example, the ace move he revealed in volume 6 which launched 16 consecutive strikes at his/her opponent, was one such move.