As much as I think a Sexual theme would be interesting, I don't believe it would be appropriate.
The Ghost idea, maybe? I think if I put some sort of spin on it it could be interesting.
Alien, is a possibility but it would probably be abstract.
Could you go a bit more in detail of what you might see in each painting? (other than sexual)
You're the artist! so that is up to you to interpret the base ideas to create from.
Do ownenwats idea if that's your style, psychedelic art and leave the sexual themes to me.