WMG / Haru Natsu Aki Fuyu

The title refers to the four main girls
Going by the kanji in their names:
  • Haruka = Spring
  • Natsuki = Summer
  • Akiho = Autumn
  • Fuyuka = Winter

http://tvtropes.org/pmwiki/pmwiki.php/WMG/HaruNatsuAkiFuyu