(5話ベース)伊理戸水斗は親の再婚を機に姉弟になった中学時代に付き合っていた元カノ、伊理戸結女を「自分たちが外泊で親に二人の時間を作る」ことを理由に、彼女をラブホに連れ込むことに成功…せっかくなので、二人の約束で結女がこの前姉弟にふさわしくない行動を取った時に溜まったのペナルティを行使することに…
が、なぜか結女のことが好きなクラスメイト南暁月に居場所がバレた模様…
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(Based on episode 5) Mizuto Irido succeeds in taking Yume Irido, his ex-girlfriend from junior high school, who became his sister after their parents remarried, to a love hotel on the grounds that they will give his parents some time together by staying out...Since it's a nice chance, he decided to use the penalty they accumulated when Yume behaved in an unbecoming manner of a sister and brother the last time...
But for some reason, their classmate Minami Akatsuki, who likes Yume, seems to have found out where she is...
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(基于第5集)伊理戸水斗成功地把他初中时的前女友,也是他父母再婚后成为他的兄弟姐妹的伊理戸结女以“他们可以通过出门给父母一些独处的时间”为理由带到一家爱情旅馆......机会难得,水斗决定使用基于两人的约定上次结女因为做出不符合兄弟姐妹关系的事情而累积的惩罚权......
但由于某些原因,喜欢结女的同班同学南晓月,似乎掌握了她们的行踪......。