A type of renSime doomed to die young from transfer abnormalities and resulting systemic degeneration. They exhibit a characteristic "stutter" in certain transfer situations and have an abnormal sensitivity to trained Gen Companions. (Source renSime)

Eventually, Klyd discovers at the end of Zelerod's Doom (Year -1 and Year 0) that those termed "Delicate" are actually a different, and useful, mutation, the Third Order channels.  Without the Thirds, the entire concept of Unity between Sime and Gen Territories would have been logistically impossible.