Mōri-kun is one of a pair of vampire bats, always seen alongside Komori-kun. These bats possess a connection to the original vampire who transformed Nyanpire by giving him blood, though the exact nature of their relationship remains undefined.

They proclaim themselves true vampires, displaying traditional vampiric traits like a craving for blood and an aversion to garlic and crosses. They once tried to feed on Nyanpire but found his blood distasteful. Together, their role involves recounting stories about the mysterious vampire who created Nyanpire, often causing the kitten significant distress or fear with their tales.

Their interactions feature frequent light-hearted bickering, with Komori-kun typically prompting Mōri-kun for agreement using the phrase "not true Mōri-kun?" after making statements. This dynamic establishes them as a comedic duo. During a Halloween episode, both bats participated in the festivities by dressing in female costumes.