In the third installment of the Seishun Buta Yarou series, Sakuta's summer takes a wild turn when he encounters Shouko Makinohara, a girl who bears a striking resemblance to his first love but is still in junior high. Meanwhile, Adolescence Syndrome rears its head once more when Rio, a stoic member of the science club, finds out she has a doppelgänger. With one Rio seeking refuge at Sakuta's place, his living situation becomes unexpectedly complicated. Add Mai's sudden decision to stay over, and Sakuta's summer break plunges into utter chaos.