Aren't they all hybrids, in a sense? According to the old legends, everybody were sea people at first, but then some migrated onto dry land and lost their ability to live underwater. Ena is the only physical difference between them, and it doesn't seem anything genetic. Considering that, anybody should be a viable choice for reenafication, should the sea god choose so. Bill's theory might be correct, in addition to the attitude of the person in question, perhaps, since it seems likely not everybody swimming in the waters right now gains ena.

Kaname was always level-headed, though in a bit different manner compared to Tsumugu, so he behaved exactly like I expected.