Maybe the chunnin exams could be held in the rain, forcing anyone that comes for it to be a ceasefire to any ill intent, or else the rain will enforce their own countermeasures. So it forces nations that would otherwise be hostile or wanting to commit murder against one another to cooperate. At least for then.
And we can fuse this with the rain diplomacy arc we talked about, so these nations that came could try and turn the rain to their side. Every nation given diplomatic immunity to be heard whilst not threat of attack