This sounds like fun, think I'll bite, assuming this thread's still active. I've never been the player in a solo erotic RPG session before, I've only GMed in the past.
System: D&D 5e (I imagine it's what you're most familiar with, and I wouldn't want to inconvenience you by pulling out something like Eclipse Phase or Tokyo Nova)
Setting: A regular fantasy setting works, but I'm flexible enough that you can add whatever twists you'd like. A fantasy/sci-fi blend, like the old Might & Magic and later Wizardry games (as well as the original Phantasy Star series on the Sega Genesis), might be fun, for instance.
Synopsis: My character is a Warlock, charged by his Patron to spread his seed to as many fertile women as possible in order to save the world from some far-off calamity. Naturally, being a hero, my character's not just going to go taking women by force, so he sets off to find and recruit women who want to bear his kids. Of course, finding such women will often require braving hardships and danger, either to find them in the first place, or to convince them to agree to his plans. And there's no guarantee that all the women he encounters will be just the regular humans and elves, either. Naturally, feel free to tweak this as necessary to fit what you want to do.
Smut to Plot Ratio: This tends to be dependent on the flow of the story, but I prefer between 40% and 70% smut.
Your Character's description: A Human Warlock, Celestial Patron (Pact of the Tome, once he hits level 3). He's tall, radiant, handsome, full of all that wonderful heroic charisma. However, in truth, it's all just his Beguiling Presence invocation. The reality is that he's a nobody, a farmer's son from a nowhere village. His Patron has convinced him of some fairly weird ideas, but he's a truly good guy at heart. However, he often feels like nobody would really like him without his Patron making him look so cool.
A character you want to appear as NPC (optional): I don't have any specific wants in this context, but I'm a sucker for cute (bipedal) monstergirls.
Venue (Discord, Bluemoon, Roll20,etc): Bluemoon
Your time availabilities: I'm available most times, MST/PST. Some nights I may be unavailable for an hour or two, and I could be out even longer on the weekends, but that's not a consistent thing. However, if we establish a set time to meet and post, I'm quite good at keeping my schedule clear. The one definite is that Wednesday nights are booked.