If Tobirama is Hashirama's brother...
Senju Hashirama inexplicably returned to the Warring States Period after the Fourth War, and Tobirama became his older brother.
Hashirama: I think Tobirama is pretty good as an older brother who dotes on me.
Madara: I met a white-haired little ninja who was pretty reliable.
Izuna: Madara seems to admire the eldest son of the clan leader opposite Shibai Mao.
Hashirama: You are obviously my little friend, Madara, please don't take my Tobirama, okay! ! !
Conception: