If only there was a way to get him to get her back... she's probably really ticklish too, because she's done a tiktok or two referencing her ticklishness.
Thank you both! Finally found it after a bunch of scrolling:
https://www.clips4sale.com/studio/28730/27949147/lali-upper-body-and-belly-button-tickling-for-18-yo-cutie-uhd-4k-mp4
In fact, it seems like they stumbled on the instant popularity of tickle challenge videos. Here's a follow-up challenge:
youtube.com/watch?v=FlNkycjFad0
I'd still call it mainstream in that there is no better place on this forum to put it. It's certainly not produced by a fetish studio. It's made by a channel that does challenges. Whether they know this is a fetish or not is up in the air.