Eiden's early history is unknown.
It is implied that at some point, he tried to take over Kodi's mind.
In Emotivity - Morality, Neisan asks a random question, to test whether Eiden would respond. He doesn't, since Eiden is long dead at this point.
Eiden is protrayed to be a chatter, fitting his role as the Narrator. He is shown to be disciplinary and concerned with perfection when it comes to his script.Powers:
- Biochemistry Scan
In Mentality, Eiden said absolutely everything that no one else said, up until his demise. Like a true narrator.