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)