[ Riku's disbelieving look is met with one of Jack's equally disbelieving ones after he says that. Jack doesn't doubt Riku's words, they're said too honestly and so Riku's obviously not a believer, but he was still able to see Jack? It would be very odd if he didn't believe in North and Bunny, but did believe in Jack when he's never even heard of him before.

Jack visibly falters, glancing down at the ground and immediately falling back on old habits and muttering to himself in his puzzlement. ] But why can he see me?

[ He almost expects to just vanish from Riku's sight then and there, but after an uncomfortable pause where that doesn't seem to happen, Jack recovers enough to answer, head tilting in confusion as he squints at Riku. ]

I'm ... I'm the same as them. Santa and the Easter Bunny, I mean. I— We need people to believe in us before they can see us which means apparently you do believe, or ... [ Yeah, he's got nothing. He doesn't understand why Riku can see him. ]