Onoderacho (Hirue Iguru), an older female who dated on the precondition of marriage, fell in love with her high school classmate at first sight 10 years ago, which resulted in the "First Love Effect" that she has always been unforgettable about her first love.

One day, the transfer student Yuuto Chiba (Yukiki Yamashita) came to his alma mater high school where he teaches in Onodera Town.Surprisingly, he is the younger brother of Yuichi (Takajo Inukai), Onoderacho's first love, and Onoderacho can't help but be attracted to Yuichi who looks very similar to Yuichi.

In addition, Onodera Town met Yuichi again dramatically at a certain cocktail party...!?