Ryakudatsu Sareta Fiancee -Koibito Masumi to Otouto no Himitsu | 略奪された婚約者 ～恋人・真澄と弟の秘密

Several years after leaving his hometown, the main character, Yuto, reunites with his childhood friend, Masumi, and they begin dating, and later become engaged. They have now started living together in her new home and are living a happy life.

One day, he received a call from his younger brother Hayato, with who he had been somewhat estranged recently since he currently lives in a rural area, that he had come to Tokyo. When I asked him about the situation, he learned that the company he worked for had gone bankrupt, so he was staying at a business hotel and coming here to look for work.

Yuto, wanting to help his younger brother, invites him to stay at his house for a while. His younger brother refuses, saying it would be bad for him to stay with his fiancé, but Masumi convinces him that there is no need to be concerned since he is also her younger brother, and she takes him home. However, contrary to her expectations, Masumi seemed confused about his younger brother staying the night. However, after learning about his circumstances, she accepts the proposal and their life together with his younger brother begins. Yuto remembered the time when the three of them used to play together a long time ago, and he wanted to continue getting along with his younger brother.

However, what Hayato and Masumi were doing without Yuto's knowledge... Eventually, Yuto would come to know this in a shocking way.