After living a privileged and indulgent life, Kiito Sonomiya enters a new school year determined to find a girl who can captivate him. His quest is granted when a dazzling black-haired beauty suddenly assaults him, leading him to seek vengeance by hunting down his attacker. All the while, a new student named Yui Kamio catches his eye with her stunning, chain-bound white hair and compassionate nature.
Through an unexpected encounter, Kiito discovers that Yui has a secret. Removing the chain from her hair triggers a remarkable transformation, unleashing a violent persona known as "Yui in Black." As he delves deeper into Yui's complex identity, Kiito realizes that the ferocious black-haired girl and Yui are one and the same.
Kiito is soon enlightened that the chain is the only means of regulating Yui's chaotic behavior. Partnering with Yui's friend Nao Ebisuno, he embarks on a mission to safeguard "Yui in White" and fend off the volatile "Yui in Black." Exposed to an unfamiliar world of uncertainty, the once-coddled Kiito is propelled out of his comfort zone and into the turbulent realm of Yui Kamio.
