#eventually izuna will have to weigh what's more important to him

[autoauthor]

Sex is a Senju Conspiracy

So, if you read the tags on my post about Tobirama being a, "well, actually" kind of person, you already knew about this idea of mine.

Here's how it would play out:

Tobirama and Izuna are fighting against some sort of third party. Allied by circumstance but not by choice. They're distracted by flirting insulting each other and the enemy shinobi gets frustrated that they're still losing and insists the two of them just bang already and get over it.

Izuna, rolling his eyes, chastises this person for actually believing sex at their age. (Maybe they escape in the confusion or maybe Tobirama deals the finishing blow so he can address the actual problem properly idk they don't matter) Tobirama is distracted from fighting his longtime rival with his intrinsic need to correct people.

First, he tries to verbally convince Izuna that sex is a real thing. Izuna claims that Tobirama is a Senju and cannot be trusted and probably has an ulterior motive. They argue in circles for a while - neither of them gets anywhere.

Then Izuna finally demands that, if sex IS real, Tobirama should prove it! Tobirama takes him up on the challenge. Cue fade to black.

Next we see the two on the battlefield and Izuna charges at Tobirama. He is pissed off because he's learned that sex is supposedly something you have to be married to do which means he'll have to marry Tobirama! He's not quiet about this confrontation which means that both their families now know that they've done the deed.

Tobirama now has to face his own clan disapproving of him sleeping with a Uchiha AND the Uchiha's disapproving of him sleeping with Izuna. He takes the only out he can see and claims that, actually, they didn't have sex as there was no penetration.

This does not actually help things. Both clans are still reeling and now Izuna is once more claiming he lied about sex being real.

(Look, Izuna may actually be that sheltered by his family. Or he could be taking the piss. OR this could be some convoluted revenge against Madara for treating him like a baby. The point is that it's left 100% ambiguous.)