Yuzuki, a high school girl is in love with Koutarou—a cram school teacher who has moved in next door. Yuzuki struggles to figure out how to approach Koutarou but her younger sister, Yui, also seems to have noticed her sister's love for him...? Leave it to Yui! The cupid of love is the 5-year-old sister! A heartwarming sisters' love comedy begins!