|Relatives||Shōta Toyokawa (deceased)|
Yui is a girl with brown hair and brown eyes. She wears a pink dress and red shoes, and keeps her hair in two ponytails with two yellow bands.
She is shy and talks mostly to her brother. She enjoys playing the ocarina and is quite good at it, although her brother teases her about it saying that all he hears is off-keys.
While going to the amusement park, Yui, along with her father, mother, and brother, died by head-on collision with a truck. After waking up as Pluses, Yui and her brother attempted to search for their parents. On one such night, as Shōta was resting, Yui sneaked off to find them. After waking up, Shōta discovered Yui being attacked by a Hollow. Yui cried out for her brother to help, but he fled in fear. After gathering his courage, Shōta returned to the park to find his sister and confront the Hollow, but she was nowhere to be seen.
While fighting the Arrancar who had attack her, Lieutenant Rangiku Matsumoto, Captain Tōshirō Hitsugaya and Shōta find Yui asleep in the park. Yui wakes up in Orihime Inoue's apartment next to her brother and the Shinigami who are communicating with Soul Society. As the group of Shinigami leave to find the cloning Arrancar, Yui and Shōta remain behind in Rangiku's care. After suddenly disappearing from her room, Yui is once again encountered at the park in the same swing she was before. When asked why is she there, she merely says that she felt like going to the park, and tells her brother that she's not scared now that he's there. Yui and Shōta are taken back to Orihime's apartment. As Rangiku and Captain Hitsugaya compare notes, Rangiku suspects that Yui may in fact be a clone in disguise. Shōta attempts to protect his sister, but Hitsugaya attempts to perform a Konsō on Yui, to no avail. Yui, scared by the situation, claims that she doesn't know anything.
With help from the Shinigami Research and Development Institute the group begins to search for energy with Reiatsu similar to her own. Hitsugaya decides to keep Yui behind a barrier, and as Shōta refuses Rangiku tells him that is for her safety as well. Rangiku gives Yui a small ocarina and asks if she would remain behind the barrier, to which Yui agreed. Yui, after having gone to sleep, wakes up inside the barrier and tells her brother that she wishes to go outside, to which Shōta says that that's what he wants, as well, but he is unable to let her out. Yui asks Shōta to place his hand in the barrier and together the two are able to break it down.
Yui leads Shōta back to the park and when Rangiku catches up them Yui tells her not to interfere. Yui releases a huge amount of Reiatsu, causing multiple Arrancar clones to appear. Yui tells her brother to come to where she is, and a melody begins to play and forces Shōta to walk toward her. Shōta yells her name out and her behavior appears to change, she tells him to get away from her while appearing to be in great pain. Yui releases and even greater amount of Reiatsu. Rangiku releases her Zanpakutō and attacks Yui. Yui's high Reiatsu is dispersed and pushes her brother away as the real body of the cloning Arrancar appears and attempts to attack him.
Yui once again releases a high amount of Reiatsu with enough power to subjugate her brother under its pressure. The cloning Arrancar says that he is surprised to see her be able to regain control of herself and forces her to turn back into a clone of himself. Yui, along with the rest of the clones, are once again united inside the original Cloning Arrancar.
As the group attempts to find the Arrancar in its hidden dimension, the sound of Yui's ocarina helps them find him. Shōta along with Rangiku delivered the finishing blow, purifying both the Arrancar and Yui's soul.