Astrid

Illuminated because one day, Nathan came to her demanding she see into his future. She did her whole "are you sure you want to know" speech so much that he doubted himself and, by the time she touched him and gasped in horror at what she saw, he'd changed his mind. Because she knows what happens, she is on his side.
Essentially, she sees him let himself die, thinks its very tragic, and sees all the good he accomplishes post-mortem.