I'll Live a Long Life to Dote on My Favorite Stepbrother!

The story of Saioshi no Gikei Mederutame, 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: ANN