If you're talking about circle-clicking rhythm games in general, probably the ad for Elite Beat Agents in Nintendo Winter 2006 Holiday Catalog, way back before I even owned a DS. Didn't get my hands on the game until 2008, but I enjoyed it enough to make myself try the Osu! Tatakae! Ouendan game that it was based off of (and of course, the sequel).
I pretty much discovered osu! through Google in 2009 after playing the shit out of those three games and still having a thirst for more. I wanted a Stepmania-like clone that was as enjoyable as the originals, but I ended up quitting nearly instantly due to how difficult it seemed... but I ended up coming back in 2012 after reintroducing myself to anime, and suddenly remembering the game's existence during a summer vacation. And I'm still here
I pretty much discovered osu! through Google in 2009 after playing the shit out of those three games and still having a thirst for more. I wanted a Stepmania-like clone that was as enjoyable as the originals, but I ended up quitting nearly instantly due to how difficult it seemed... but I ended up coming back in 2012 after reintroducing myself to anime, and suddenly remembering the game's existence during a summer vacation. And I'm still here