The leader of the Beast Friends. A cocky and foul-tempered but cute kitten. He is characterized by strong pronunciations like ending sentences with "-kkang!", "-ttang!", or "-ssio!". He was originally a house cat living in a wealthy home, but he left thinking a real man should live as a stray, only to give up after a week. He tried to go back but forgot the way, eventually settling in Yoo Sumin's house after a chance encounter. He carries a secret regarding his birth and his father who disappeared during his childhood. When angry, he shouts "Hey, you f*cking bastard!" in his usual tone.

A sly Shiba Inu who is well-versed in the ways of the world. He loves adult videos and is characterized by always communicating via handheld signs. He is an influencer with millions of Instagram followers and calls Sumin 'Hyung'. Despite being a Japanese breed, he is fiercely patriotic towards Korea, claiming Dokdo is Korean territory. There is a heartbreaking story involving his mother, from whom he was separated as a child, behind why he only uses signs. When pissed off, he grabs Saedaegal by the neck or even tries to eat him. However, he uses polite speech with most human adults, excluding nuisance characters like Yoo Sumin.

A pigeon who suddenly appeared one day by slamming his head into the window of Sumin's studio apartment. Usually dim-witted, but very skilled at delivering harsh truths. He has a habit of saying "Who are youuu?". He has a unique trait where he becomes incredibly intelligent if he receives a strong impact to the head. Although he has wings, like a typical pigeon, he rarely flies and mostly walks around. However, he can fly when the moment calls for it.

Like Ttang-ttangi and Saedaegal, she is a polite-speech character. Her name comes from her habit of ending sentences with "-syumdyang!", "-syumgyang?", or "-hamdyang". Jjijji (an experimental guinea pig) gave her the name Syum-dyangi. She refers to Yoo Sumin as "Master".

The eternal butler of the Beast Friends. He is 24 years old, lives in Uijeongbu, Gyeonggi-do, and is a college student majoring in Korean Language and Literature at Naksung University. He raises the Beast Friends in his studio apartment and is constantly pushed around by them. In terms of character dynamics, he is in the Go Gil-dong position. While he has a wimpy personality, he is warm-hearted; though he always gets annoyed or angry at the Beast Friends, he inwardly cherishes and values them deeply.