I have feeling that the sage's brother might be the Death Ripper, I wont bother searching manga proofs and stuff its just a tought I had, seeing how kishi writes this story, this could be true. I mean, people only remembered Hagoromo as time passed and not his brother, that's weird because Hamura was Kaguya's fkin son, on a level with his brother, well who knows, these are my toughts, discuss it further if you wish.