Place it right after the entrance cut, once the character is fully visible, then follow with a reaction sound to sell the moment. A Teleport Sound just before the cut sets up the arrival, and a JoJo To Be Continued cue after it can close the scene on the reveal.
About this sound
This short 1.8-second clip is Saitama speaking the Portuguese line Você apareceu mesmo in a calm, matter-of-fact voice. It feels dry and understated, like a quiet call-out rather than a shout, which makes the arrival land with deadpan humour. The line comes from One Punch Man, presented here in its Brazilian Portuguese version.