Yes, Kaya does do a lot of the doing, but there's also some doing of Kaya being done.
>_o @ variations of "do"
In Transient, Current, and Corroded Cage it's very obvious.
But, I disagree with you about NVC. Because, well, he's the one making the babies, therefore assuming a passive, female role. But it is empowered. Yeah, Kaya, you are woman, hear you roar. Or something.
But I kind of see Kuro Ageha as a sort of prologue/part of Corroded Cage. I think they have a lot in common, lyrically. Both deal with themes of captivity, torture, and so on, with the narrator in the passive position.
...And note how carefully I'm avoiding directly refering to sex and BDSM.
Edit: And also, if Kaya were the one doing the doing, I don't think he would be beging to be swished away or whatever.
Edit Edit: Kaya seems to like butterflies a lot, even back in Isola. (Pst, we need some kind of lyrical stuff on his Isola work)
And all I know about the insect is that it is black, it is common in japan, and they caterpillars are really really cute.
http://www.asahi-net.or.jp/~ak5t-kmn/papil/t96sp95m.jpg
See?