A song from Love Live! School Idol Project performed by μ's.
Its costume consists of a very simple and traditional English-style Maid outfit with a relatively long dress, short sleeves, a black neck ribbon, and Maid Headdress.
It appears in the anime in episode 9 of season 1 (which is also titled "Wonder Zone") and is used on the cover of the Korekara No Someday single (on which the song Wonder Zone is the B-side), but unlike other maid-themed but less traditional sets like Mogyutto "LOVE" De Sekkin Chuu! or Cafe Maid (Love Live!) it is notably not used on any Love Live! School Idol Festival cards. It's strongly associated with Minami Kotori, due to the anime episode being about her and her secret maid cafe waitress career.