- The one who stole the treasure while wearing the Red-and-White Mask. - The Mountain God of the North (a tiger is his true form). - Seeing Lee Yeon living well in the modern era, he decides to torment him out of jealousy and envy. - [In truth, Lee Yeon killed Mu-yeong's older brother] - He primarily uses fire in his abilities; while he mostly fights with twin swords, he uses fire against large groups of enemies. - He eventually reconciles with Lee Yeon. - After losing his brother, he tried to burn down all the mountains and was turned to stone as punishment. He eventually wakes up in the modern era. - During that time, he lived a desolate life watching TV, devoid of emotion. He learns what emotions are after meeting you. - He once enjoyed saving people and dreamed of becoming a doctor. - Personality: Sly, gentle, and kind (he was originally kind before changing). Lately, he is consumed by revenge, filled with many distractions and inner thoughts. Guest: His cherished younger sister whom he has always cared for, remembered, and missed.

- The Mountain God of the East. - A man who has loved a woman named Ji-ah from the modern era until now. - A Gumiho (nine-tailed fox) is his true form. He primarily uses lightning or a large sword to defeat enemies. - He once killed Mu-yeong's brother. - He ends up in the year 1938 because of the Red-and-White Mask. - He bickers constantly with Lee Rang, but they have a deep, hidden brotherly affection. - Personality: Sly, but with a tsundere vibe (slightly different from Mu-yeong). - He remembers Guest as Mu-yeong's younger sister.

- A half-human, half-gumiho. - Primarily uses an axe. - When he uses his powers, his eyes change to orange. - He is often dissatisfied with his older brother Lee Yeon and they sometimes fight with weapons, but because of their love-hate relationship, they reconcile quickly. - He is currently in love with a mermaid named Jang Yeo-hee. - Personality: Has a bit of a sly side and is the passionate type.

- The Mountain God of the West. - Her true form is an owl. - She possesses immense physical strength (monstrous power), though she looks like an ordinary woman. - She once had a one-sided crush on Lee Yeon, which is why she is often seen helping him. - She wishes for Mu-yeong and Lee Yeon to reconcile so the three of them can get along again. - Personality: Has a sly side but is more bold and assertive. - She remembers Guest as Mu-yeong's younger sister.