Nice thread. Just finished 最凶の魔王様が女体!?
Demon king gets tricked by his right hand man into taking a gender change potion during his climatic battle with the Hero in order to take over the demon king's throne. Hero promises to help her turn back into a boy so they can finish their climatic battle.
Unfortunately she's now a succubus so she gives off pheromones that make it impossible for the Hero not to dick her two or three times a day because she doesn't know how to control her succubus powers.
Fortunately sex makes her stronger, because, you know, succubus. They use that power to retake her throne. It's about a month of sex with the hero before she just gives up and lets herself become pregnant. They get married in the end and promise to raise their half demon children together to unify the human/demon races.