I'll re-say what some of my suggestions to buff it incase someone goes to this page. (These could be op so keep in mind these are simply suggestions)
1. Homing Rain
An upgrade for bouncing rain that makes the balls homing instead of bouncing
2. Ability to use bouncing rain while running/walking
At the moment the skill completely slows you down for a slow worthless attack, the proposal allows the use of the attack whilst running/walking (could be inactive if you have homing rain skill)
3. 2x Faster use
Make the skill happen at 2x the speed
4. Huge defense increase whilst you are using the bouncing rain attack
Half second or so after you press M and the attack is preparing, have a large defense multipler for then.
Not all of these would have to be added but I do think #2 and #3 are absolutely necessary to make the skill viable in any way.
You also can't use the skill if you have 25 or less MP for some reason when it only costs 10 MP to use, please fix this @Robby
Also a general attack increase would probably go along way if some of what I suggested gets added. Feel free to disagree with I wrote or add onto it.