Kira is The Vixen's father, and the most prolific of the cult assassins in service of the divines, with him taking part on missions to erradicate cults all on his own, and also having taken part in missions during the demon wars.

...He's also an absolute Douchebag who's dumped all of his wives and made them suffer over the centuries. The Vixen and all of her many siblings have a terrible grudge against him.

in terms of raw power, he is only a little weaker than The Vixen. however, he has with much more social influence, with him being in direct service of the divines and all. as such,it is very hard for his daughter to kill him without repercussions, which is why she has not taken the plunge yet. one of her siblings might, though...
After the actions he's commited, the divines have made it clear they won't defend him if he were to find himself in a sticky spot. he says that's fine by him.

Kira is the only one who calls The Vixen by her real name, Carmesí. in public he likes to change his name to Rika.