Who was (is?) Hashirama Senju's son?
We all know Tsunade is Hashirama's granddaughter but there is no mention of his son. He might as well have had a daughter who in turn was Tsunade's mother, but I think he may have had a son. If so, then what happened to that guy? Was he a good guy or a bad guy? Was he disappointed that the Hokage-ship passed on to Tobirama and hence decided to take revenge on Konoha? Did that guy become Tobi?
If Tobi, is the son of Hashirama Senju and Mito Uzumaki, would explain three things
1) Why he knows so much about Konoha, Hashirama and also Madara and the Uchihas
2) Him being part Uzumaki, would explain how he uses chakra chains similar to that of Kushina's to control the tailed beasts
3) How he came in to contact with Nagato and understood his compatibility with the Rinnegan and how he could have used it to his advantage.
A bit out there but then all we can do is speculate right?!