Miu, the younger sister of the womanizing delinquent Ryuta, gives in to his pressure and makes a date to meet up at night. 
In order to protect his overly kind-hearted sister, her twin brother Mio disguises himself as her and heads to the appointed place! 
However, on the way there, Miu gives him a "cuteness supplement" that has an unexpected effect, and Mio's body unknowingly transforms into a woman's! 
He was supposed to punish the vile Ryuta with his fists, but his frail female body is unable to resist!? 
This is the story of a tsundere brother who cares for his younger sister and falls into the trap of becoming a transsexual! ♪