@nohd https://urasunday.com/kengan/comic/event002.html this is from the official site, it's in japanese but it confirms theres a sequel coming this month
even before chapter 42 this was foreshadowed back in chapter 29 when Nogi wasn't surprised Kazuo predicted which fighters were advancing from the prelims. Great job by the author
So he didn't actually teach the advance, seems like it just got activated. And with the real name being "possessing spirit" maybe its something that lies dormant in some people as opposed to being an actual technique you learn? Interesting development