Youpi was the strongest among the Ant King's Royal Guards in terms of physical talent and raw bodily strength. In terms of physical attributes, he was also the one closest to the Ant King—a super monster composed entirely of magical beasts.
His Nen Quantity was dozens of times greater than that of Morel, one of the Hunter World's experts. Knuckle had called him a monster of a man.
He possessed incredibly powerful combat instincts, but he was not particularly intelligent and was easily deceived.
In the original story, Pouf had once persuaded him, but because of his loyalty to the Ant King Meruem, he ultimately told the truth.
In other words, among the Ant King's Royal Guards, Pitou was completely loyal to the Ant King and carried out Meruem's will with all her heart.
Pouf was likewise loyal to the Ant King, but his imagination ran too wild. He easily concocted all sorts of ideas and acted in ways tantamount to betraying the Ant King.
Youpi's intelligence was too low. If he followed Pitou, he would carry out Meruem's will like Pitou did; if he followed Pouf, he would be swayed by him. But he himself would absolutely never do anything harmful to Meruem.
Meruem's earlier words had been intended to stir something within Youpi—perhaps self-reproach and guilt. Youpi, Pouf, and Pitou were known as his three most loyal Royal Guards. That was no empty claim; there was no doubt about it, and they took pride in it.
Unlike Youpi, Pouf would carry out his own imagined interpretation. Although his methods would indeed make for a good ruler, that would only be a ruler of the Chimera Ants.
Or rather, a ruler cold and merciless toward all life beyond them. To Meruem, that was nothing more than a killing machine.