Geyser is a weapon that appears in Zone of the Enders, The 2nd Runner, and The Fist of Mars. In Zone of Enders and The 2nd Runner, when the weapon is used, a cluster of grenade-like weapons are thrown out. These grenades cause minor damage to and stun enemies that are hit. After hitting another solid object, the weapons each emit a "geyser" of energy which can further damage and stun enemies. The spread of the grenades can also be controlled depending upon the amount of pressure put on the circle button.
In The 2nd Runner, during the "kill spider save civilian" mission, Geyser is recommended by ADA to be used on friendly LEVs in order to slow their attack, which reduces civilian casualties.
During the Battle for Aumaan, Leo also recommends using Geyser on damaged friendly LEVs, so that he could see it and quickly come to its aid. Once Geyser is used upon a damaged friendly LEV, Leo would immediately come to its rescure, restoring the LEV to its full health. It seems that Leo/Vic Viper can do this as often as you require, and is not limited by subweapon gauge like Jehuty. Also, Vic Viper repairs LEV far quicker than Jehuty. So Geyser is by all means a smarter choice to repair friendly LEVs than grabbing them and using your own weapon energy to do it.