Obviously, Itto's enjoying himself, if the eager way he continues sucking him off is any indication (which it is). The fact he's going quicker than Sizhui would've encouraged him to is both incredible and slightly concerning, the latter because he's worried Itto might choke from his enthusiasm, though he's still being very careful to not move his own hips for that exact reason. (And, being fair, to avoid accidentally shifting wrong and catching those sharp teeth.)

When the other male withdraws, Sizhui's head lifts up, mouth dragging at an agonizingly slow pace back to the tip of Itto's dick, his tongue flicking over the slit. While he does pull off, he tilts his head, briefly catching his partner's gaze before tilting until he can part his lips and leave wet, lingering kisses along his length, teasing the sensitive skin. “Good, and you may,” he affirms, increasing the pace of his hand that's stroking him. “Come for me, Itto, then we'll try something else.” More is exactly what he'll give him too; the flat of his tongue drags from root to tip, he takes Itto's cock back in then begins bobbing his head again, working earnestly toward bringing him to orgasm, and it should be clear where exactly he wants Itto to come.