I don't understand why humans health and mana are limited to 999 as humans are limitless. We reach, build, learn and gain. If you work to move forward you will always have gains no matter what, there is no plateau in life and there has to be a relation between humans and the demon race just like humans to animals and demons to demon animals. The demon races don't seem to be limited at all in terms of hp and mana, but life span is affected. Mana should be able to be used to extend ones life in a positive way obviously with some negative effects that accumulate over time just like regular aging.
Honestly if it were me, so long as I am happy, healthy, have people I care about I can live on and on. I love to discover, learn, hear stories, tell stories and the like. I could do that forever so long as there are those I can get along with. I would definitely do a familiar or marry the demon king as they seem to innately love the fated ones no matter what and it kinda seems like the fated has feelings for the demon king or they are quickly developed.
It is unfortunate that there are so many flaws in the writers manga, but that is a lot to think about when creating your own world with its own rules. Though I do think the author got it right with the balance of knowledge and power. You can't have people advancing too quick as that generally leads to bad things. They need to move moderately in all directions and fields.
This kinda felt like and intro to the story up until now, but I don't know how much more the author can put into the story at this point besides saving liliam
@ThyUnsuspicious
Pretty sure she has the option to return with memories and mana at the end. It would be nice as it could benefit our medicine. Who knows she may even be able to unlock magic on earth for other people. If we have a natural disposition to high mana then everyone would live 300 years which is bad considering how everyone except whites and the Japanese breed way to much like africans and muslims. Luckily magic is forbidden in islam, but you know they'd bs it into "mohammed knew about magic first and how to use it, but he banned it because it would lead to many deaths"