[@floodtalon]: Okay, it's daytime and I am distinctly less tired. Having consulted with the others, this is the conclusion we've come to:

A final statline of C+ C A E E C is fine on our end.

The bigger point of contention was how the Manslayer skill was set up. I can see that you're trying to justify how his NP appears to work in-game, but we can also chalk that up just as easily to a technique that the dude knew. Super damage to a Servant or gibbing a Master on the spot with a nick is a bit absurd.
An alternative to setting this up is that wounds dealt by Izou take longer to heal (especially given how Servants have a knack to just shrug off chip damage after a while out of combat). If the wounds stick, then he has more utility rather than a built-in Zabaniya as a skill, which could also lead to more interesting situations in the long run.

(Dude has a habit of biting off more than he can chew, anyhow.)

Think that's about it, though. The others will say if there's anything left to be ironed out.