Tobirama was a victim of child abuse. That happened when he was a kid, he was abused by an uchiha. He can't remember by who Because subconsciously he suppressed those memories for so long as a defense mechanism. Maybe that subconsciously affected how he felt about Uchihas. But unfortunately the leader of Uchiha clan; madara had a thing for him. Madara despite the fact that found tobirama annoying pain in ass found himself wanting to spend time with him and be close to him. Sometimes he just had a urge to touch tobirama's skin, caress his hair, kiss on his skin but he always held himself back. But what if one day he didn't and that triggered tobirama's memories that he suppressed for long time? (Take the role of whoever you want)