Yomiel's Fiancée is a character who is never seen in the game.
After Yomiel's death, his fiancée killed herself to join him. However, she wasn't aware that Yomiel was still "living" due to the radiation of the Temsik fragment. By the time Yomiel regained his body and found her, she was already dead, leaving a note saying, "I'm coming to you, Yomiel."
It is revealed at the end of the game that her name is Sissel, and that Yomiel in fact named the protagonist after her.