Yuzuka is an office worker at a cosmetics company. With her wedding to her older coworker and fiance just around the corner, she feels like she's walking on air each and every day. But when she discovers that he's been cheating on her, just like that, she's back to square one... Then, as she struggles to hold her broken heart together and look for a new apartment, she somehow ends up living together temporarily with her childhood friend and corporate heir Katsumi, whom she hasn't seen in 10 years! Katsumi had always treated her like a dear, younger sister. But when Yuzuka notices what a fine, mature gentleman he's become, the pounding in her heart just won't stop!