Jerme is a sociopath who joined Nergal due to his love of killing. He does not expressly agree with what Nergal is planning, but couldn't care less as long as he got to "feed his blade".
He is the boss of one of the two possible versions of the chapter "Pale Flower of Darkness". You play his version if your physical units are higher-leveled then your magic units. He uses the Light Brand.
He appears as a morph in the last chapter, wielding a Runesword.
In personality, he is an evil and arrogant man. His only desire is to kill as many people as he can to sanctify his psychotic needs; especially his blade. He is also known as the Death Kite. He harbors a deep, incredibly creepy love of killing; he wonders aloud if Lyn's flesh, cut to ribbons, would be as soft as silk.
The Light Brand Jerme uses doesn't necessarily "feeds the blade" from a person's life, only to cast Light Magic from the distance and to attack in close quarters. Until the last chapter, it was replaced with the Runesword; that's the only time he can "feed his blade".