She is the mother of Komasan and Komajiro and deeply loves and cares for her two sons. She is commonly written to by Komasan, and they both wish to take care of her in the off hand chance she visits (as shown in an episode where Komasan goes to a sushi place to see if it would be something she'd like).
In the third movie, Koma Mom was summoned by Nathan Adams to save Kanami from suffering a fatal fall when the world turned real. From a flashback, it turned out that Nate got the Medal from Komasan as a thank-you gift.
"Koma" comes from "komainu", or guardian lion dog. "Kaachan" refers to the relationship she has with the Koma brothers.