takeoffyourbra
honestly author I can think of lot of thinks he can do with rain, acid rain, hail storm rain that strikes like bullet shots and kills. raining fire and brimstone and sulphur (Like bible), nagato's rain jutsu for sensing, healing rain. Well all this so long as he can conceptually manipulate the very concept of "Raining". maybe someday he will be able to rain meteors as well. Unless you intend to keep him constrained in only manipulating rains of water only (Please don't do that). Maybe make him do all that mentioned above when he reaches the level of SSS. By the way with merlin's Infinity spell alone he is pretty much invincible. Add all that mentioned above and he will be someone no less powerful than odin or thor.