The second in the series, and no better or worse than the first. Asai made an interesting choice by having Hiro (Heaven's trainer, her only real friend, and the object of all her lusty thoughts) begin dating Karen. Especially since Karen begins her time in the books as a likable and normal person.
And Heaven learns to turn herself invisible? Sort of. Ninja voodoo, you know. (Oy.)
I don't know if I'd feel comfortable recommending these books to someone else, because they're pretty blah, but if I can get my hands on the rest of the series, I'll read them.