I have just read your status update.
Equip quantum slice, the ability to perform quantum slice in the air, and geyser palm and play an aggressive, mid-range zoning game.
Katar toss starts up and travels so fast that opponents cannot distinguish the regular version from the amplified version so they will be blocking your projectiles a lot.
While they are blocking, use Rain's excellent movement to dash in and throw, jump, force whiffs and punish with f+2,d+4, etc. Use quantum slice once in a while because of its big aerial hitbox like
@Wigy said.
If you struggle getting in, EX diving quantum slice is a safe, half-screen "dive kick" that resets neutral. This move must be one of the best in the game.
1,3,3 is your auto-shimmy string. The last hit can actually be crouched so mix up with 1,3,4, which is flawless blockable, or 1,3 xx EX katar toss, which is completely safe.
1,3,3 xx EX geyser palm 2,4,2 xx geyser palm is an easy combo that does good damage.
For all other strings, including 1,3, use the EX geyser kick to launch.
Rain seems very good to me thus far... unless you equip bubble. LOL. I really believe he needs katar toss to be effective.
Maybe geyser palm could be replaced by tidal wave in some match ups, but I need to play a lot more games to come to that conclusion.