Lemme tell you, having chibi-fied people in the background related does not endear me to whatever anime this is supposed to be from. It usually takes a very strong premise, prior viewing of said anime, or seeing the chibi form in something like an omake or 4Koma for me to tolerate them.
The song itself is annoying, too, as was the beatmap itself. Replaying this later with other mods added on will not be fun.
For Osu!
Osu! is a rhythm game based off of Osu! Tatakae! Ouendan! and the American release Elite Beat Agents. In these games you click circles to the rhythm of the song. Osu! also has different rankings you can shoot for, with SS being the best (Hit every note and have 100% accuracy). THere are also mods like Hard Rock, HIdden, FLashlight, and Double Time/Nightcore if you want to increase the difficulty even more.
There are 4,503 views in 935 videos for osu!. His channel published over 1 day worth of content for the game, roughly 21.26% of osu! content that JonathanScarlet has uploaded to YouTube.