The Kaiju Soldiers were a group of anti-Kaiju infantry created by the PPDC, and later utilized by all Defense Corps.
The human Kaiju Soldiers were deployed against the Kaiju Suction, where both Ruby and Sapphire Gem saw them attempt to slay the beast, though it sucked the hundred-strong group/platoon/squad into its mouth, where the soldiers were presumably killed when Kaiju Blue corroded the armour through various cracks and tears caused by debris. That said, the resistance of the armour was celebrated as Suction's blood was so powerful the Kaiju's corpse quickly dissolved. They were quickly utilised across the world, with K-Stunner bazookas being commonly used.
Three to four months after the Human version's introduction, many that looked like armored Precursors accompanied the Kaiju, with Cat. 5 "carrier" Kaiju arriving ashore and disembarking thousands of soldiers, who would attempt to lock up a Jaeger. Some had M-Immobiliser (Mundo-Jumbo Immobiliser or CHITTER-CHITTERCHITTERCHITTER in Precursor) cannons which, when fired into the joints of a Jaeger, temporarily caused a synaptic overload which locked up the joint. The Jaeger Thunder Cloud was destroyed when soldiers systematically locked up the Jaeger, eventually swarming the Conn-Pod and killing the pilots. They also tore apart the remaining foundations, leaving no trace left.
Destruction of the Kaiju they were "linked" to (never the carrier, as it always died soon after releasing the soldiers) caused the soldiers to melt into acid.