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

Alba is reincarnated as the son of a poor nobleman with a rare condition that renders him unable to use magic, which is typically a defining trait among nobles. He joins the duke's family and reunites with Orsis, a person he had a close connection with in a past life. Alba's past memories resurface, revealing the reason for Orsis's loss of smile, and he decides to find a way to live a longer life to ensure their relationship endures.