Looking at some art recently, this is a recent discovery for me, but it's definitely something I'd like to give a try.
Basically, as the title indicates, my character would be a gelatinous "goo girl" for your character to gleefully fuck. As for the setting, I could see it as working in fantasy, sci-fi or something with an anime/manga bent.
I love the idea of the character casually going about with a big load of cum floating around inside them for everyone to see. Although it seems as though the RP would be mostly smut, if you're into something more, we can definitely discuss that.
Some of the anonymous comments on the artwork really grabbed my attention, so if you agree with any of these, I'd love to hear from you!
"HELL YES! This looks like such fun!"
"Goo girls are just MADE to cum inside of!!"
"Lucky! I'd be sure to blast a huge load deep inside her too!"
"Wow, I can't put into words how hot it would be to see your own cum floating inside her goo-body!"
"I'd LOVE to empty my balls inside this sweetheart!"
"Even if she's blue, imagine how awesome it would be to keep her turned white!!"
"OMG! What a great idea! Practically KEEP her white so everyone could see!"
If you're interested, please send a PM
Edit: I have actually started working on an idea involving a fantasy setting in which the basic idea is that your character would encounter the goo girl as a very rare race/being, and they would become adventuring companions.