At Sakuradamon High, Seiji "The Mad Dog" Sawamura's right hand is infamous for its tremendous power which intimidates many, including girls. Rejected repeatedly by girls, Seiji humorously expresses his intent to rely on his right hand as his sole companion until graduation. The next day, Seiji wakes up astounded to see his once threatening right hand has transformed into a miniature girl now called Midori Kasugano, who confesses to having been in love with Seiji for a long time. Despite wanting to reverse the transformation, Seiji's blunder at Midori's house causes them to keep the predicament a secret till they find a solution. Thus begins their unusual relationship, finally giving Midori the opportunity to be with her beloved man.