On a rainy day, the elite salaryman Amakusa Ryo almost falls down some stairs when he is saved by an ordinary high school girl named Arima Ichika. Ryo was dizzy from not eating breakfast, which worries Ichika and she offers him her lunch then runs off. Later when Ryo gets home, Ichika is in his living room and he finds out that she is actually his sister Rio's classmate. Ryo wants to thank Ichika for saving his life and offers to kiss her...