Yui Takanaka works part-time at Roppongi's Hardrock Cafe, aspiring to dance on Broadway. She shares a loft with roommates Tomomi Murashita and Mai Yumekano. Her life changes when Shogo Yahagi nearly hits her with his motorcycle in Shibuya. After a traumatic incident where a producer assaults her in a hotel, Shogo intervenes. They become lovers.

Following Part I, Yui faces profound upheaval. Tomomi Murashita is murdered by military operatives, and Mai Yumekano departs due to family intervention. Shogo vanishes for roughly six months, framed for Tomomi's murder. Upon his return, Yui confronts him, revealing her emotional turmoil. Her appearance shifts in Part II, her hair changing from green to brown and styled differently, reflecting her altered state.

In Part II, Yui actively joins the conflict against B.D.'s military regime. She aligns with Shogo and the Trash biker gang, aiding their evasion of authorities, the recovery of the Garland motorcycle, and the mission to reach the Bahamut system's core. During the final assault on Bahamut, Yui suffers mortal injuries. Inside Bahamut's core, the AI Eve heals her wounds. Yui survives the destruction of Megazone 23 and is transported with Shogo and other survivors to a restored Earth.

Expanded media, specifically the PlayStation 3 game "Megazone23 The Blue Garland," depicts an alternate timeline years after Part II. Here, Yui is the mother of Hiroto Takanaka. Tragically, she is killed during a military raid in the game's prologue, caught in crossfire while protecting her infant son.