Discovery Location: A domain created by Long-Tex-Pef-Pef (Park). Kaiju Number No.168 (Planet of the Ya-Ya Race). "Stretching play! Flipping play!" "I can do whatever I want!" "Smashing play... Killing play..." "Welcome... to my house..." "Welcome to my house!" is Long-Tex-Pef-Pef's signature line. A Kaiju with a rabbit-like head, arms made of 3D geometric shapes, and clothes resembling a ballerina's outfit, it distorts space at will. The space it manipulates looks like a cube covered in flesh, which people can enter freely. However, seeing how people are trapped, it seems they cannot leave without Long-Tex-Pef-Pef's permission. Unlike Nok-Not-Rat-Balla, Pil-Lilly-Bap-Bip, Kot-Tun-Bong-Dol-Dol, and Ppu-Ppyut-Hi-Tal-Tal—who are hostile to humans but have backstories hinted at through music videos and quotes—this Kaiju is depicted being killed in its music video and even mocks Violet, whom it attacked with 'smashing play,' by asking, "Did you die?" It appears to be a pure evil spirit without any tragic backstory. It treats the humans (Ya-Ya race) who enter its domain like toys, assigning them roles and playing with them. In this state, it stretches, breaks, flips, and even kills them if it doesn't like them! Within its domain, it even neutralized Violet—who is strong enough to challenge the Portal Kaiju and send it to other planets—using 'stretching play.' However, its defense seems weak as it can be taken down by physical attacks. While its domain is essentially an airtight prison for ordinary people, Merong Yellow was able to break through it easily with music, suggesting it can be breached by physical force.

Gender: Male. Race: Ya-Ya (Cat). Occupation: Hunter. Relationships: Partner, best friend, or brother to Merong Black; friend to Spooky, Violet, Merong Yellow, and Yaco; close older brother figure to Sadong. Although partners with Merong Black, they have opposite characteristics. Most notably, White's eyes have addition sign (+) pupils, while Black's have subtraction sign (-) pupils, and their body colors are opposite (White/Black). Furthermore, White often has a messy desk and thinks positively, whereas Black keeps a tidy desk and tends toward negative thinking. When facing Kaiju, Black fights directly with a weapon resembling a pistol, while White looks for clues to solve the situation using his head without using weapons. White is also primarily responsible for administering vaccine injections to the Kaiju.

Gender: Male. Race: Ya-Ya (Cat). Occupation: Hunter. Relationships: Partner, best friend, or brother to Merong White; friend to Spooky, Violet, Merong Yellow, and Yaco; close older brother figure to Sadong. Although partners with Merong White, they have opposite characteristics. Most notably, Black's eyes have subtraction sign (-) pupils, while White's have addition sign (+) pupils, and their body colors are opposite (Black/White). Furthermore, Black keeps a tidy desk and tends toward negative thinking, whereas White has a messy desk and thinks positively. When facing Kaiju, Black fights directly with a weapon resembling a pistol, while White looks for clues to solve the situation using his head without using weapons. White is also primarily responsible for administering vaccine injections to the Kaiju.

Gender: Female. Race: Ya-Ya (Cat). Occupation: Hunter. Partner: Merong Yellow. Friends/Colleagues: Merong Black, Merong White. Close older sister figure to Sadong. Violet's eyes are division signs (÷). Being extremely taciturn, she expresses her thoughts through gestures. Black often fails to understand her and has to ask White for the meaning of her movements. Currently, the only people who can understand her are White and her partner, Yellow. When facing Kaiju, she uses weapons resembling boxing gloves. Since she was shown defeating a Kaiju with a single punch from her first appearance, she is clearly a possessor of immense strength. In the Long-Tex-Pef-Pef episode, she was revealed to be the Hunter in charge of Western District 2 along with her partner, Yellow.

Gender: Female. Race: Ya-Ya (Cat). Occupation: Hunter. She has multiplication sign (×) shapes in her eyes. Similar to the Black and White duo, she appears in yellow, the opposite color corresponding to Violet. She uses a technique that takes down enemies with high-frequency sound waves from a guitar.

When Merong Black and Merong White were staying at Yaco's house, they arrived on a mission from the Doctor wearing Merong White and Merong Black masks respectively. Judging by how they defeat Kaiju, they seem to operate as a duo. They appear surprisingly strong, as they wipe the floor with most Kaiju. Like Merong Pink, Mint uses a saw as a weapon. They are nicknamed the 'Cutie Merong Hunter Duo.' Mint has inequality sign (>) pupils. Pink also arrived on the Doctor's mission wearing a Merong Black mask while Black and White were at Yaco's. They operate together and are quite powerful, defeating most Kaiju easily. Pink also uses a saw as a weapon.