Meteor Rain

Meteor Rain (メテオレイン) is what X receives upon defeating Rainy Turtloid in Mega Man X6. In normal fire, it creates a sphere of water that bounces and hits the enemy over and over if it stays there. Charged up, X shoots a sphere of water up, which creates more orbs of water to fall diagonally.

This weapon is Metal Shark Player and Illumina's primary weaknesses. Dynamo is also weak to this weapon - using Meteor Rain on him will stun him momentarily, and a follow-up hit will cause him to drop 200 Nightmare Souls. 

Trivia

 * As stated above, Metal Shark Player is especially weak to this weapon (alongside Ensuizan). This may seem to be an extremely bizarre weakness, considering that Player is a shark-like Maverick, but one must take into consideration that despite that fact, this boss manipulates and uses metal as a weapon. Metal is generally susceptible to water and moisture, causing it to rust. Therefore, based on being a Metal-type boss, Metal Shark Player is weak to water weapons.
 * Despite being a Water-type attack, Meteor Rain is somewhat similar to Astro Crush from Mega Man 8, being that Astro Crush uses Comets that rain down on enemies, as Meteor Rain, when Charged, rains down water meteors.

Counterpart to this Weapon

 * Ensuizan