Hitotsu Yane no Shita, Boukei no Konyakusha to Koi wo Shita.

The more they think it's hopeless, the more they are drawn to each other. This is a pure love story about a high school boy who falls in love with his deceased brother's fiancée and a woman who projects the image of her beloved onto her fiancée's younger brother. It is a tale of two people who share the same pain, destined for a happy ending. High school student Nanase Minoru loses his only relative, his older brother, and ends up living under the same roof as his brother's fiancée, Mirumachi Shiho. As he navigates the delicate distance that makes them neither family nor strangers, Minoru gradually finds healing in Shiho's enveloping kindness. However, feelings that he absolutely should not harbor begin to sprout in his heart, and Shiho, who has also lost her beloved, feels the same… To become irreplaceable individuals, not mere "substitutes" for each other—this is a story of how their shared sorrow eventually transforms into love. This pure love story chronicles the days leading to happiness for a high school boy who falls in love with his brother's fiancée and a woman who sees the reflection of her beloved in her fiancée's younger brother.