Mamahaha no tsurego ga moto-kano datta 4 (Kadokawa Sneaker Bunko) [Light Novel]

[Machine Translation] Mizuto and Yume, who became siblings after their parents remarried, are former lovers. They are now getting used to being a "family," but memories of those days come back to them from time to time, and they are still worried about each other... Halfway through their summer vacation, the Irido family returns home to their father's side of the family. ( Mizuto-kun~! Long time no see! ) Mizuto is greeted with a hug by his relative Enka Tanezato, a neat and tidy-looking young woman. For some reason, Mizuto is obedient to her, but Yume guesses - this person is Mizuto's first love! The third summer festival arrives, and Yume's ex-boyfriend and ex-girlfriend, who thought they had put their old love behind them and accepted their current relationship, are still in a whirlwind of unresolved feelings. The ex-couple is very upset by Yume's decision to return home for the summer vacation!

親の再婚できょうだいになった水斗と結女は、元恋人同士。“家族”らしさも板についてきた二人だが、ときおりあの頃の思い出が蘇り、やっぱりお互いが気になる日々で―。そんな夏休みも半ば、伊理戸一家は父方の実家に帰省する。「水斗くんじゃ～ん!!ひっさしぶりぃーっ!!」水斗をハグで出迎えたのは、親戚の清楚風陽キャお姉さん・種里円香。なぜか彼女には従順な水斗に、結女は察する―この人、水斗の初恋相手!?昔の恋は振り切って、今の関係を受け入れたはずの元カレと元カノに、未練が渦巻く三度目の夏祭りが訪れる。結女の決断に元カップルが大いに揺れ動く、夏休み帰省編!