Pop'n Music is a Japanese rhythm video game that has become a liking to a niche of the English side of Hatena Haiku. The Japanese side knows a bit more about it as most of it is in their language, they had it first, and there is a wide variety of visuals they have there which our English friends just cannot really offer right now.
Most games in the series are in the arcade box format however there are also a few for systems like the Play Station Portable or the Nintendo Wii. Either way, expect a lot of button pushing at the right time.
All else which can really be said about this collection of games is that it consists of a wide variety of characters that are a whole bunch of different creatures coming from all over the world. Hard to say how many there are for sure or what their names could be as some of them are in Japanese which the English side would need more speakers to understand and perhaps find even more that the Wikis of this crazy language does not possess.
The game was originally discovered by Red when she played it at a certain anime convention. She expressed her love for Zizz soon after and a little later the obsession spread over to Parascout and Robot.