I'LL LIVE A LONG LIFE TO DOTE ON MY FAVORITE STEPBROTHER!

The story of Saioshi no Gikei wo Mederu Tame, Nagaikishimasu! follows the struggle of a player to protect his favorite character, who gets reincarnated as his older brother-in-law in a simulation raising game - however, the player is reincarnated as the younger brother who was meant to die. (Source: Anime News Network) — Description from AniList community (anilist.co).