Saikin Gitei ga Kyodo Fushin Desu. (Cinderella Novels)

[Machine Translation] Fuyuko Wakamiya is a college student who has never been in a relationship, let alone had a boyfriend. On the advice of a female friend who knows about her unfortunate love life, Fuyuko decides to try having sex by herself in her room. However, her brother-in-law Yosuke, who is a perfect superhuman, witnesses her doing so! Fuyuko then has to explain the situation to Yosuke, who is even more upset than she is for some reason, but this turns out to be a new and spectacular misunderstanding! And after that day, the relationship between the two, who had been close sisters-in-law, started to clearly change...? The cool brother-in-law's misunderstanding, doting love, and possessive desire accelerate in this extremely sweet love comedy!

彼氏どころか恋愛経験もほぼ皆無な女子大生、若宮冬子。そんな残念過ぎる恋愛事情を知った女友達の助言により、冬子は自室で一人エッチに挑戦してみることに。だが、間の悪いことにその行為を完璧超人な義弟の陽介にばっちり目撃されてしまった!その後、何故か自分以上に動揺する陽介へと事情を説明することになった冬子だが―逆にそれが新たなる壮大な勘違いへと発展!?そしてこの日を境に、仲の良い義理の姉弟だった二人の関係性は、明確に変化し始めて...!?クールな義弟の勘違い×溺愛×独占欲が加速する、激甘系ちぐはぐ義姉弟ラブコメディ!!