Personally, rather than an 'instant down' action, I was hoping for something to skip a turn without raising your defence or evasion. Something to use before you unlock the actual sex-actions or full submission.
At current, once you have enough hp you become invincible, since you regen faster than it can be stripped away.
All you can really do is run around till your exhaustion hits like, 50%, or spam the moves that cost spirit to end the fight faster.
I wanted her to be knocked down with full spirit, so she'd have a nice long scene before being defeated.
Also, if she cums in battle she gets knocked down, but you are forced to get up because your only available move is 'breathe' which auto-recovers you. A way to make her stay down (like you can if she gets knocked down normally) would be nice.
Aside from that, Orc-boss seems to have a move that puts her into unique knockdown state. She lands flat on her back in a way that I haven't seen any other enemy manage.