Princess Knight Concedes to Cum

A cyclops ambush should have been the end of you, until a swordswoman drops out of nowhere and cuts the thing down in one strike. You follow her instead of running for town, catch her bathing, and when she mistakes your dick for a weapon, you talk your way out of it by challenging her to a "mating duel." It works.

From there the story jumps ahead: you're settled into a demon lord's castle with Reika, the once-legendary swordswoman now living as your personal slut, until her old comrade Astrein, the goddess of war, shows up to check on the quest and finds her companion thoroughly ruined.

You spend your time reading through the fallout of that duel and the visit that follows, pushing the story forward and, eventually, working on winning over both women rather than just one. It's a visual novel, so the winning mostly happens in dialogue and in bed, not in menus.