blood kain is a fun move to putz around with
i would suggest checking the combo thread for BK combos, you can ask your above question in the "General Ragna discussion" thread, or just check the ragna 101 info thread. i use my BKs like empty jump ins. i don't do it often, but when i do it's out of the blue, and my opponent is surprised momentarily, and i take advantage (i.e. empty otoshi's with Sakura in SSFIV)
HOPE THIS HELPED!