Talk:Monster Girl Encyclopedia World Guide II: Demon Realm Traveller's Guide/@comment-29602226-20190319231721/@comment-27950421-20190320001031

Well Incubi and Heroes have limitless potential, potentially beyond that of the gods. (Hence why the gods made monsters and started the unendinv conflict between man and monster and put limits on human potential.)

And mamono grow in power along with their husband. (With a sufficient amount of time and sex, you could feasibly have any mamono reach or surpass the demon lord in power.)

Also, most spirit realms don't have a physical connection to the materiel plane, so they are impregnable to anyone with sufficient magical tallent unless the owner/creator of the spirit realm opens a gateway of some sort.