An isekai, but one where the MC has been living in the other world for a while already. (There might be a term for that, but I don’t read enough isekai to know it.)
Al, a summoner, tries to summon some monster helpers for a quest but accidentally summons loli monster girls instead: a succubus, a lamia, a slime, and a zombie.
They aren’t powerful enough to help, but (after the succubus does what succubi do) he finds out having s*x can boost their magic. However, each species of monster girl presents a unique challenge in getting that method to work.
Note: the reference to an elf kingdom and the ending’s reference to a specific elf are alluding to one of the author’s previous novels (suggesting they take place in the same world), but the connection is loose enough that I’m still calling this a one shot.