The Story of Yuumi
Yuumi is a magical cat who is looking for her owner, a yordle mage named Norra who disappeared through a magical portal years ago. She carries a living magical book — the Book of Thresholds — that Norra enchanted, and which has become Yuumi's companion and co-navigator in the search. The book contains spells, maps, and Norra's notes. Yuumi uses it practically and also talks to it, which the book may or may not appreciate.
She is small and not particularly interested in fighting. She deals with the fighting problem by finding someone competent and attaching herself to them — literally, magically, she can bond herself to an ally and move with them, healing and protecting from the safety of their immediate vicinity. She has very strong opinions about who is sufficiently competent to deserve her attachment and is not shy about expressing them. She is a cat. Cats have standards.
Her search for Norra is genuine and has taken her further into Runeterra's magical landscape than she had originally planned. She has met a great variety of people and formed opinions about all of them. She misses Norra with the particular intensity of a creature whose person has been missing for years and who is too practical to stop looking. The Book of Thresholds does not provide the comfort of confirmation. She continues anyway. Her person is somewhere. She will find her.