Mika calls Yūto late at night to invite him to Haruka's birthday party on the evening of October 20. On the day of the celebration, Yūto goes to Akihabara to buy a gift and bumps into Nobunaga. After buying the gift, Yūto goes home and is fetched by Hazuki and Nanami to be taken to the party venue on an island far away together with Ruko and Yukari. On the island, Yūto meets up with Mika and Haruka. After meeting some of the guests, Yūto starts feeling insecure about his gift and social status.
春香の誕生パーティへの招待を受けた裕人は、彼女の好きなアニメのフィギュアをプレゼントしようと秋葉原で購入した。そして超音速ジェットで彼が連れてこられたパーティ会場は、赤道直下にある乃木坂家私有のリゾートアイランド。パーティが始まるまで裕人は、水着姿の春香や夏美たちとバカンスを楽しむことになるが…。
하루카의 생일에 초대받은 유토는 노부나가의 도움을 받아서 '덜렁이 아키' 피겨를 생일 선물로 준비한다. 생일 당일이 되자 하녀들이 나타나서는 전용 비행기를 타고 남국의 어떤 섬으로 유토를 데려간다.
