Ore wa Mada, Honki wo Dashite Inai

The main character, the fourth son of a noble family and known as the disgrace of nobility, is forced to take over the household after his three older brothers, all members of the same political party, die in a meteorite incident. His remaining older sister renounces her family ties and officially becomes his foster daughter, addressing him as "father," in an effort to have him assume leadership and prove his true capabilities.