One of the breakout stars of the inaugural skateboarding event at the Tokyo Olympics is a champion who's not even competing.

On Monday, Ryo Sejiri, a TV commentator for NHK, was in his element, giving the kind of move-by-move analysis that's all too common in sports, but with his distinctive flair.

"Yoooooooo," exclaimed Sejiri after Chinese skater Zeng Wenhui landed a particularly complicated trick during Monday's street event for women.

"Yiiiikes, that's hot," Sejiri added, highlighting the move's difficulty. "That is sooo sick," he repeated later as Japan's Momiji Nishiya and Funa Nakayama battled for gold against Brazilian prodigy Rayssa Leal.

Sejiri, a 24-year-old skateboarding champion, joined NHK's first-ever Olympic skating broadcast on Sunday to provide commentary on a sport that remains entirely new to many of the public broadcaster's audience, which includes many older viewers.

Speaking in a more relaxed and casual tone of Japanese than NHK's normally staid style, Sejiri said during a Sunday broadcast that a skater had been "seriously grinding" during a practice session the day before, prompting a confused response from his fellow commentator.

Sejiri explained that he meant the athlete was really working hard and giving the routine their all. The more straight-laced announcer, who has since become the skater's foil, was quick on the uptake.

"So now, that athlete who was indeed 'grinding' yesterday is coming up," he said.