Kind of reverse Hanahaki AU where the disease develops based on the intensity of the feeling rather than the lack of reciprocation, and where the feeling which causes it changes anytime a new Mokuton wielder is born.
Basically what I was thinking was that while every Senju has the seeds from which Hanahaki sprouts in their lungs/stomachs* it takes a live Mokuton wielder for them to actually start acting. Maybe because the seeds draw chakra from both their vessel and the presence of someone with Mokuton? Idk didn't think that far.
(With the stomach thing I was thinking mostly of this sengen fic since it's awesome as fuck and I regularly reread it. It also neatly explains the more scientific possibilities of Hanahaki that I'm too dumb to fully understand and how it survives in the human body)
Anyways, picture this; The village is built. Izuna is alive because I'm an unrepentant sucker for fluff, and everything that follows is more or less peaceful, though filled with the canon-typical political hiccups and stuff.
Nobody ever thinks too hard about why some Senju always have a cough, or how Hashirama refuses to use his kekkei genkai unless absolutely necessary, or how, contrary to their reputation, the Senju compound is actually sparse in terms of plants. They chalk it up to inter-clan weirdness, because what else could it be?
Until the first non-Senju gets Hanahaki. Until Konoha's hospital doesn't know how to help them.
Until Hashirama appears less and less in public, up to the point he's either never seen at all, or whenever he is seen it's from a significant distance.
Tobirama, naturally, despises the isolation his brother is more or less forced into, even if he understands why.
Cue him looking for a cure, except the only way to find one is to have a live specimen, but he's not about to just steal a patient from a hospital, that'd just be a quick way to ruin the peace etc etc.
So instead he forces himself to develop Hanahaki.
And, since Hashirama is the current Mokuton vessel, that means he has to fall in love. The best way to do that would be to find someone high enough in rank, as well as smart enough he won't loathe them at the end. (since losing the feeling which developed the Hanahaki is one way to get rid of it, and that'd just make for a poor test subject, wouldn't it?)
And then blah blah blah Madatobi where Madara tries to keep Tobirama from accidentally killing himself with his research while also having to keep the village afloat despite the constant tension and absence of Hashirama's charisma and blah blah blah
