Name: Unknown. Rather, more like she doesn't have a name at all.
Age: Late teens, from 15-19. She doesn't quite know herself.
Appearance: http://danbooru.donmai.us/posts/1204756
Personality: An unusual sort of person who lacks defining qualities. Tends to be easily influenced by people and is always checking her phone and notebook for the things she wrote in them. Seems to be almost whimsical, ignoring things from the previous day as if nothing happened. She's the type to follow explicit goals and what not, and seems rather easy to read. Rather eccentric and is not very good at dealing with people, but tries anyway. This is due to the nature of her origin, "Tabula rasa".

Background: Was a little girl diagnosed with memory problems after her origin awakened around her tenth year of living. At the same time, her powerful potential as an Esper awakened, and she was shipped off to Asagami Fujino as her caretaker despite arguably needing more of that herself. Nevertheless she proved herself to be dependable, and simply accepted the offer to give herself a new sense of "purpose". Not like this matters much. After all, she lacks the ability to define herself.

Supernatural abilities:

Origin: "Tabula Rasa"
Not exactly in the philosophical case of all people are born lacking knowledge, but rather close. In short, her identity is basically a "blank slate", with no identifiable properties whatsoever. Every day she wakes up without a personality, although she has established a routine and can remember roughly a week's worth of memories. Every experience is new, and fresh, only to be wiped away the next day. As such, she is very inconsistent and prone to influence.

ESP: Identity Theft
By stealing the core concept of an object or person, she can attempt to define herself. For example, if she encountered someone with a sword, she could steal the sword's concept of "being a sword", preventing it from harming or cutting her as a sword is supposed to do. At the same time, she can assimilate it into her own identity, thus becoming a "sword" with increased durability and the ability to cut objects. This works on all objects (including spells, mind you) and living beings, although living beings resist having their identity taken away. In addition, mystery also makes it harder as well. However, a simple concept like "leg" can be stolen, and she can work her way up by stealing so many concepts from her target she can eventually steal their identity because it lacks anchors, or what defines it. Gaia does eventually fix the missing identities, but by then it is usually too late. Also, due to the nature of her Origin, the concepts she steals are wiped away as well the next day.