Talk:Incubus/@comment-45424649-20200802121304/@comment-10429980-20200802213002

World Guide 3 explains more about the link between lifespan and power, but outside of undead (who are not more powerful but rather have a entirely different nature as a living thing) lifespan does not appear to actually become infinite. After all, the whole point fo the soul marriage spell when used on those who are not undead is to ensure the couple can stay together when they eventually die. Also the multiple references to how monsters stay beautiful to the very end of their lives.

But back to World Guide 3. Runya mentions that since mana is life then having more mana means having more life, thus beings with more mana tend to live longer. Since monsters have their mana enhanced by having a husband, one can presume that even "shot lived" ones get longer lives in this way. Likewise, in a harem the monsters would all presumably get a lifespan equivalent to whichever member of the harem is most powerful thanks to mana sharing via their husband. I think KC may have mentioned something like this, but I can't recall where right now.

But yes, monsters with shorter lifespans can be assumed to be more fertile to make up for it.

And to clarify, all monsters normal lifespans are noted to be at least somewhat longer than humans. None appear to have actual human lifespans.