I was recently reminded of old characters and games I was in, and kind of felt like trying to do something similar as an RP.  Given that the old idea was a tabletop RPG, things may change from there, as needed.  The system used was...not very good, anyway, so it's not a huge loss, to be honest.  Totally stealing some of the setting though. 

[b]Lovecraftian magical girls[/b]

May really be more "magical girls," if I hew close to the original concept.  It is the near future.  Humanity has advanced, and part of its advancements are due to the development of technology influenced by what some might consider ancient magic.  See, some of those ancient tomes and magical practices had hint of greater cosmic truths within them, and a few enterprising scientists managed to connect them to actual scientific theory.  The result: whole new branches of science and technological development.  Also, a broader acceptance that magic is real, that the universe is even bigger than we know, and mythos critters and magical rituals actually exist.  

So yeah, magic is real.  The Old Gods are real.  And so-on.  Player characters would be what amounts to eldritch horror versions of the Guyver, right down to fighting a megacorporation controlled by monsters who can take human form (and an entire cult dedicated to Nyarlathotep).  Or, at least that's the usual expectation.  The magical girl part would come in by just making the player characters young women who were accidentally dragged into a secret war by a ritual gone wrong.  This wouldn't change what they are, though.  Unless everyone would prefer an even sillier treatment.  

Whatever the case, the premise is roughly thus: in a cyberpunk future version of the world according to Lovecraft, humanity's learned just enough to be dangerous.  A group of young women end up joining in a secret war between a megacorporation that has been corrupted from within by a dark cult, and those who know this.  Enjoy a slow descent into madness, while trying one's best to right wrongs and triumph over evil while also going to school.

An alternative to a scifi future would be to set things more in the present, and possibly go for a lot of 1920s style, where it makes sense.  

General influences: Deus Machina Demonbane,The Guyver, various darker magical girl series

Most of my other ideas are smaller in overall scope, so they might work better as 1x1 things.  

[b]Cyberpunk and transhuman...stuff[/b]

Much less thought here, but I like cyberpunk settings and particularly exploration of themes like what it means to be human in a transhumanist world.  Cybernetics, AI, and so-on are commonplace, but people are still people, even if their bodies are no longer flesh and blood.  Could just be character study things, Shadowrun style criminals, or something else.  Really, I just have some characters I'd like to play who are AI or cyborgs and not much to do with them.  Some of my influences in the genre would be Eclipse Phase, Blame! and Tsutomu Nihei's other manga, Expelled from Paradise, and Battle Angel.  

I've got a couple weird superhero-ish character ideas touching on some of these things would could use a home, but that's about it from me for now.  

And that's probably about it for now. Pretty much any of these could go into adult territory, if one would be interested in such.  Though beyond some things like love and sex for full-body cyborgs, nothing would inherently be 18+ either.