Talk:Troll/@comment-24768935-20140609051529/@comment-25035274-20140611210134

Cross has actually thought of this(never mind the part about the Demon Lord trying to give mamono the ability to bear male children). In the here and now, we know of two definite ways to extend someone's life. The first is for that person, man or woman, to become an incubus or mamono. As you pointed out, many mamono live a long time, and becoming an incubus can increase a human man's life span to be closer to that of his wife.

The second option is to purchase(or get through less scrupulous methods) mermaid's blood. Their blood can extend a human's life without transforming them. Mermaids in this setting are friendly with just about everybody and regularly trade with other monsters and humans. The mermaids get the things they want or need, and mamono and humans get a bit of their blood.