Yuumi was a small Demacian that didn't have any real talents. Her swordsmanship, athletic prowess and mental aptitude weren't very noteworthy, which made her the target of being teased and tricked by her fellow countrymen. The only talents that she had was the ability to read magical texts, though, this was forbidden in her country as magic was considered a taboo.

She blamed the way she looked for limitations and struggles in life. Living in pain and being the center of everyone's criticism every day drove her into despair. On the night of a full moon, she ventured out of the village to seek some momentary refuge. Her venture had led her into a forest that she had never took notice of before. With tears in her eyes, she wandered the forest until she took sight of a strange light. Curiosity got the best of her and she followed it deeper into the forest. To her surprise, the light led her to a small Yordel wizard, that of which had a stature even smaller than her. The wizard greeted her, gave her a warm smile and asked if she wanted to play with them. Hearing such a kind offer from someone who didn't ridicule her warmed her heart and she accepted.

After hours of spending time together, the Yordel Wizard took notice of Yuumi's plight. To relieve her troubles, the wizard lent her a magic book rather than of playing a foul trick on her, like turning her into a mushroom as most Yordel Wizards of the time were known to do. The book went into details about altering one's appearance to have them grow in stature. Ecstatic with the promising results that awaited her in this book, she thanked the Yordel Wizard with excitement then proceeded to head back into her village, keeping the book well hidden from her townsfolk. Without hesitation, she gathered the necessary ingredients for the spell and got to work drawing the runes into the floor of her room. The magic circle she drew lit up and in a moment's flash, the spell was cast upon her. But to her dismay, something contrary to what the book described began to happen to her. Her skin began to sprout fur and her body began to shrink, clothes sliding off of her body. In a moment's time, the lights from the circle dimmed and Yuumi looked into a mirror to get a better look at what happened to her. To her dismay, a small cat stared back at her when gazing at her reflection.

Shocked by the events that befell her, Yuumi traveled into Runterra, utilizing the knowledge she had gained from magical texts to levitate the book that changed her, in hopes that she could find someone capable of turning her back into her original form.