It All Started With Pompompurin

Hasegawa Kouta is a completely average second-year high school student. He feels as though something is missing in his life and that it's impossible for someone like him to have a shining school life. Then one day, as he's out with his friends, Kouta encounters a missing little girl and she gives him a Pompompurin sticker for helping her find her mom. This reminds Kouta about how he used to love Pompompurin as a kid, especially because of the giant stuffed Pompompurin his beloved grandmother gave him as a birthday present, but was forced to cast that aside due to peer pressure. However, at school he picks up a lost My Melody keychain and realizes it might belong the very flashy and popular Mizuno Ryu, how is this possible?