Saw it on YouTube, I was basically jumping around and clicking at random videos and I stumbled across an osu! video. It was a replay from some top-tier player, don't remember who, but I remember thinking, "Woah, this game looks like it'd be addicting, I'm going to try it out."
i love rhythm games, and i searched "best rhythm games for pc" on youtube and Osu! was number 1 on some guys top 5 list. Lol i didnt know then that i would become a hardcore player of this back then. XD
I was looking for Earthmind - Kaleidoscope on YouTube. All of the hits contained the word "osu!", so I clicked the first one and it was a replay of someone playing. I got curious, searched for osu!, watched some Cookiezi videos, the rest is history.