Explaining to a friend
Banging on the door to Madara's place during the dead of night was the last thing Tobirama thought he would do when he woke up.
But that's what ended up happening.
The pain in his eyes and his headache was still unbearable but at least he was well enough to move and get help.
This probably had to do with his experiment with the chakra injections. Probably. No. It definitely did. Was this some sort of delayed reaction? Likely. He needed help, and he didn't want to bother his brother about this, not after the incident today. Especially not after what happened today.
This was a long shot, but it was better than having to face his brother. (He was still angry at Hashirama, despite the pain that he was now facing.)
Madara's reaction wasn't what Tobirama was expecting, but Tobirama didn't even know what to expect to begin with.
Izuna had left a few weeks before, after the attack on the village. The same attack that resulted in Tatsuma's death. So he didn't have to worry about any confrontation with the younger Uchiha.
Izuna hated him and Tobirama didn't blame him at all. The Senju had nearly killed in battle. But that was war. Tobirama wished that he could have befriended the younger Uchiha but Izuna wasn't comfortable with him and he didn't want to force a friendship.
Madara was his friend though, and he trusted Madara with this.
But this was still not what he was expecting, whatever his expectations were.
But it certainly didn't include Madara serving him tea and calmly discussing what he's done, and the experiment along with it. What happened with Tatsuma..
The fact Tatsuma had left Tobirama his Sharingan as he was dying.
That wasn't a pleasant memory to remember with all the emotions he was feeling.
But it needed to be explained.
Madara would eventually tell Hashirama, that was a fact. Tobirama didn't have a definite time for when.
He really didn't want to deal with his older brother. He just didn't.