Hey, question for ya. Do you think you can do a reverse of your story in a sense. What I mean is this: The Mc before death, was a well known guy for being a Demon in the sheets but grew bored for reasons he would not say.
Apon being reborn and learning his role in reviving all the near dead/extinct species, we learn that his interests lies with things not being human or human looking.
Also, when he has sex, he is the top, he gets stronger depending on how laid the monster is and how strong they are. And the monsters are usually back home taking care of the eggs and kids while the MC is going being a pocket monster collector- I mean a monster harem master- I mean a good husband/Demon lord.
And last thing, The 'Hero' of the story (male or female, I don't care) apon encountering the mc tries reason with him. It fails, then plan B of kill the mc fails because the soon to be parents rescue the mc cause he was in over his head.
The Hero finds the mc hot after a while of observing, which are claimed for research purposes, and after being called boring to their face for being human, they try to find a way to transform into something else to win over the MC.
They will save they are doing it to save the world, but they are lying.