User blog comment:Xilinoc/Ch. 608 - whatever the title of this one is/@comment-24913480-20141204195428/@comment-5398287-20141204234549

Going point by point here:

The whole darkness thing seems to be a secondary aspect to Ichimonji. Since the main power is removing names with ink, the darkness essentially acts as the "inkpot", so Ichibei draws on it for his power. He's not really controlling it so much as just utilizing it. In that way, the relationship between abilities is still there, it's just a bit more fleshed out in Shikai.

I don't think Yhwach was necessarily going to steal Ichibei's techniques, Zanpakuto, etc., but just his spiritual power.

And yeah, Aizen's got nothing on these fellas. He was all brute force when it came down to it.