The Kirbons are primordial elemental particles, which along with leptons, electrons and protons were the building blocks of all matter.
The Kree Kleaners are a variety of Kree soldiers deployed to deliver judgement in name of the Kree Empire. They are artificially conceived inside a pod once it's activated by a beacon signal. Afterwards, the baby's inception and gestation is accelerated and they grow into an adult into a matter of hours. During this process, they are instructed by the Kleaner combat tutorials on their way to their objective. A Kree Kleaner is also accompanied by a group of self-regenerating combat drones, which help the Kleaner locate and eliminate their target.
When Captain Marvel unwittingly turned on a Kree tracer used by her mother Mari-Ell, a Kree desertor, the tracker sent out a beacon that activated one of countless Kleaner pods floating in space. A Kleaner was deployed to deliver Mari-Ell's death sentence for treason. The pod landed in Canada, and the Kleaner made its way to Harpswell, Maine. Mari-Ell managed to fend off the Kleaner, but she returned and took her son Joe Jr. hostage. Carol and Mari-Ell confronted the Kleaner in the center of Harpswell, and Mari-Ell was fatally injured blocking a spear meant for Carol. Deeming her mission complete, the Kleaner used Mari-Ell's tracking device to discorporate herself.