|“||I suppose... going back on my promise, even to an enemy... felt like a defeat, in a way.||„|
|“||I am a shield. Protect the King with my life.||„|
Menthuthuyoupi is part chimera ant and part magical beast. Despite this, he is mostly humanoid in shape. He appears as a muscular human with red skin. He does not wear a shirt. He has the ability to change forms and took on several appearances. One such was a monstruous form with many eyes. He later appeared as a centaur, and also grew wings. After giving his energy to Meruem, he became a shrunken fairy-like version of himself.
Menthuthuyoupi was the most straightforward of all the Royal Guards and possesses a strength that comes from his lack of an ego. He was a Chimera Ant without an iota of human genetic material within him, caring less about his identity as an individual. He was quick to cease unnecessary thought, focus on prioritized goals, and acted upon his instincts—allowing him to be completely selfless and devoted to the King. However, his simplicity was both a boon and burden. His belligerent, vehement, capricious, and irascible nature made him a fine, yet a variable soldier. His naïvety contrasted the eccentricities of his fellow Royal Guards, much to Menthuthuyoupi's confusion.
However, Menthuthuyoupi began to mature and change during his battle with the Hunters, Shoot, Morel, and Knuckle; and he began to act selfishly which was contradictory to his nature. He began to rapidly "mature" during the battle, becoming a cunning strategist who uses his rage at the ideal moments. At the end of the battle, Menthuthuyoupi had matured to the point where he reached his "Rage Incarnate" form and was even "thankful" to the Hunters in helping him achieve this form. Because of this, he gained a level of mercy towards others and spared the life of enemies which he would have killed in the first place without a second thought. Thus, Knuckle lost the drive to fight him since he could no longer see Menthuthuyoupi as a villain. After donating most of his body to the King, he agreed not to remind him about Komugi so he and Shaiapouf would get to enjoy their closeness with him.
Menthuthuyoupi was the last ant born to the Chimera Ant Queen. He was named by the Queen herself. After the king was born and the queen died, Youpi, along with the other Royal Guards, joined the king to take over East Gorteau.
Unlike the other Royal Guards, Youpi had little role in the conquest of East Gorteau or the selection ceremony, as his skills were only really useful for combat. He spent his time near the king. He was the simplest of the guards. When asked what the king's name should be, Youpi mearly stated that it was not his place to say. When Shaiapouf pondered on whether questioning the king's judgement was an act of betrayal, Youpi merely said that Pouf "thought too much".
After Meruem injured himself and Neferpitou was tasked with healing him, Youpi guarded the central staircase that led to the throne room. When the hunters attacked the palace, he was the first one they encountered. He immediately fought back to protect the king, and was hit with Knuckle's "Amortizing Power Redirector" (APR). At first he couldn't see this since Knuckle was invisible. He immediately engaged in a fight with Knuckle, who was invisible with Meleoron, and Shoot. He defeated Shoot easily, forcing Knuckle to reveal himself and fight. Youpi then noticed APR and tried to get rid of it.
As he fought Knuckle, he got angry, causing his first transformation. Knuckle thought that he could take advantage of this and attack Youpi while he was transforming. Youpi, however, anticipated this, and used it as a trap for Knuckle, but was hit with Killua's thunderbolt before he could kill Knuckle. Youpi tried to chase Killua, who escaped using God Speed. After this, Youpi battled Knuckle and Morel, who made several smoke clones of Knuckle to confuse Youpi. Youpi transfored into a centaur form. He threatened to kill Morel if Knuckle wouldn't release APR. After Knuckle released APR, Youpi joined Shaiapouf to find the king.
Pouf and Youpi found the king dying from the explosion of Miniature Rose. They both gave their energy to heal the king. Youpi became a miniature version of himself, and developed an empathic link with the king. The three of them went to defeat the hunters. The king asked Youpi why he failed to kill the hunters after APR was removed, and Youpi said he thought it would be dishonorable to kill them after promising to spare them.
Since the king lost his memory, Youpi and Pouf plotted to kill Komugi, who they thought was harmful to the king, before the king could remember her. As Pouf and Youpi left the palace, Youpi stayed, and was confronted by Welfin. Welfin asked if Youpi remembered his past. Youpi said he didn't but then died from the poison from Miniature Rose.