Menthuthuyoupi is the least humanoid of the King's Royal Guards, yet despite this fact his physical appearance is loosely human. He has a bulk musculature and a manly frame, but with irregularly shaped ears, animal like legs and razor sharp teeth. He has prominent facial bones and constantly squints his eyes. Youpi has dark red skin and short black hair slicked back on his head. Youpi is the largest of the Royal Guards and scarcely clothed, only wearing a pair of skintight black pants.
Menthuthuyoupi is the most straightforward of all the Royal Guards and possesses a strength that comes from his lack of an ego. He is a Chimera Ant without an iota of human genetic material within him, caring less about his identity as an individual. Youpi is quick to cease unnecessary thought, focus on prioritized goals, and act upon his instincts—allowing the ant to be completely selfless and devoted to the King as such. However, his simplicity is both a boon and burden. Menthuthuyoupi's belligerent, vehement, capricious, and irascible nature make him a fine, yet a variable soldier.
Little is known about Menthuthuyoupi's past, but in fact he is the only non-human hybrid among Chimera Ants as he inherited genetic material from both his Chimera Ant mother and a Magical Beast.
Menthuthuyoupi is the last of the Royal Guards to be born shortly prior to the King's breach and, as all, he is also personally named by the Queen. Most of the time, he stays quiet and still along with the Royal Guards for the King's orders, excluding when he was ordered to stay with him much to the King's annoyance and send him fly with one strike of his tail.
As the Chimera Ant Extermination Team charges into the palace of East Gorteau, he was instructed by Shaiapouf to stay at the main stairs and kill any intruder that comes into contact with him. He is engaged in battle against Knuckle and Shoot, Shoot taking the lead against him. Knuckle, hidden within Meleoron's ability, wait for the right moment to strike him and activate his ability. Shoot, about to be killed by Menthuthuyoupi, is saved by Knuckle who successfully land a blow on him and activates his Nen ability.
Knuckle tries to take Menthuthuyoupi alone as Meleoron left and Shoot is almost dead, but proves to be more than what he could take. Menthuthuyoupi, enraged and confused where the other guards and the King are, accidentally activates his Rage Blast and explodes, giving time to Knuckle to search for Shoot. Menthuthuyoupi finds Knuckle once more and deceives him into believing he was about to explode again. Knuckle tries to use that moment to punch him, but Menthuthuyoupi reverts to his original form. Just when he is about to land the final blow, he is struck by Killua's lightning.
Shocked at the fact that he can't sense Killua's presence, Youpi goes on a rampage against him, but is unable to land a blow and receives several more electric shocks until Killua runs out of electricity. As he was starting to chase him, Killua disappeared again, making Menthuthuyoupi realize that there is one more enemy with the ability to hide his presence or teleport, and that's why he couldn't feel anyone the first time he was struck.