Ore wa Mada, Honki o Dashite Inai

A bizarre twist of fate befalls the protagonist, who is the fourth son of a prestigious family and has been deemed the black sheep of the family. With his three older brothers all tragically killed by a meteorite while in the same party, he is tasked with inheriting the family estate. His elder sister disowns herself and legally adopts the protagonist as her foster child, calling him "dad" in hopes of encouraging him to lead the family and showcase his true potential.