For now I Have two ideas of character for you. ^^

The first is simple and may be you already plan something similaire: A demon who want play with Akane womb or other bodt part with the sigil. A demon who know a lot of way to have fun with the womb.

The second: I like the way of Akane put the feet of Leane inside her womb.... but I wonder, what about a character who can separate body part and still feel them and move them? Or may be have leanne like this? Like that, that would be fun to have some body part separate inside the wombe of Akane.

I have other idea but I need to fix them before to propose you, tell me what you think. :)