An ML who knows what he wants and does not hesitate to go for it! Courting his guardian, the Demon Queen, with intentions of marriage! A heart melting romcom! Now serialized. Link: https://mangadex.org/title/28892/maou-sama-to-kekkonshitai Let the fluff wash over you!
Wonder if a hero will come along and end up in the harem or get sacrificed to make ml into immortal demon
Screw harem! And what hero? This gunna be Demon Queen x servant-slash-ward, their blissful life together, and the children(all 8 of 'em) they will make... tropes be damned, racial differences be damned, age difference be damned, lifespan disparities be damned! Hero-kun better not take up any panel space! He can be forgotten side character or cannon fodder 4 all I care. If he interferes, I'ma gonna slay him meself!
If a demon Lord story is there a hero is bound to come who might be an airhead loser or ruthless asshole depending on circumstances the author has placed into the character. If a hero is female she can become part of a harem or even if hero is/not female they can be sacrificed or something to aid the human to become an immortal demon or something