Ellie has an air of mystery, as she is freqnently busy or tardy and tends to arrive at the academy late. She is alike to Fuuko in many ways, however unlike to Fuuko; she wishes not to get close to people because she fears of their reactions. For these reasons, Ellie has a tendency to be taken to the 'little sister' role, as commented by Chlotz of her 'sister aura'. She is often excited or flustered when God's Gift agrees to her role of being a sister; although truly she wishes for him to not think her as eccentric and wants his affection, the same way she thinks about him.
May contain spoilers
Ellie originated from Gazel Village orphange, although there was no detail of what happened to her parents. She struggled with the large amounts of star energy she contained. Most children at her age would've gone through medical procedures although for being an orphan, she didn't. This caused her body to break down and she began severely bleeding. A boy on his errands noticed her alone in a sandbox, noticing her look pale. When Ellie suddenly began bleeding, he held onto her and told her,'don't die!' despite them being strangers. By the time it came to other peoples notice, she was already 'dead'.
Ellie revealed to have lived because of the ether from him. It calmed her wild star energy and put her into a fake death. Although she mentions,'normally I would've died from such injuries', which adds onto a further mystery of her survival. After her fake death, Ellie was moved to the city Shelgard to be appointed by the Church. There she went through the medical help she previously couldn't have. She also became a stillblood, as a result. At some point, she went along with Lucian, obeying the order of the church to hunt down heretics, opposers of Gracia. Ellie moved to the academy, along with her side role and tried to adapt a normal life; just as well the duty of being a bringer of star children.