Nephilim

A Nephilim is an individual who was born as the result of a Demon breeding with a human.

Overview
Humans have notably bred with demons in the past, with many Exorcists descending from them.

First generation Nephilim inherit the most power from their demonic parent, however over time, the Demon blood becomes diluted to the point where the descendants of Nephilim will be indistinguishable from ordinary humans.

A Nephilim has a longer lifespan than a human, with long lived Nephilim living about two hundred years. This is not always the case, as some have bodies that break down quickly, like those under demonic possession. Rin Okumura, as the first Nephilim of Satan is an unknown factor, his lifespan being a mystery, even to those with vast knowledge of Demons such as Lewin Light and Mephisto Pheles.

Trivia

 * Nephilim in other popular media are depicted as angel-human hybrids, but this could be a possible reference to how they are descended from a fallen angel (i.e., a demon). There is also how the concept relates to Cambions from European mythology, who are half-demon half-human beings.