For me, it was the Kizuna AI saying fuck you clip. I watched her a bit and moved on after getting bored without realizing there are more vtubers. In hindsight I ran across vtubers a lot afterwards. I watched a translated clip of some babiniku talking about how his life as a grocery store clerk sucks and saw the nigga compilation thinking the same thing as
>>14554224. I masturbated a bunch to NLO's but also others' stuff, especially to Suisei and Sora, all the while thinking Hololive is yet another gacha game I have zero interest in. The Suisei getting discovered by her parents clip may or may not have been popping in my recommendations for some reason, but if it did I refused to watch it as is my wont when Youtube seems to shill something too hard or if I tried to watch it, I probably got filtered by her voice right off the bat.
But it wasn't until I learned there is an international incident caused by a pair of anime streamers that I really started digging into the entire scene to see what the hell it is all about and got hooked by Suisei's voice. My digging into vtubers happened to coincide with one of those phases where I don't feel the need to masturbate, so when the phase where I very much do started, it was a weird feeling to realize that I had already been finishing to my oshi for months.