Sphere is a J-pop idol unit made up of voice actresses who are all managed by Sony Music Entertainment's Music Ray'n subdivision, under the Lantis music label GloryHeaven. The group debuted in April 2009 releasing their first single "Future Stream", which was followed up with the June 2009 release of "Dangerous Girls" theme used in the opening animation of the PlayStation Portable game "Ken to Mahou Gakuen Mono 2" (known in the US as "Class of Heroes 2"). As all four are voice actresses, their music is frequently featured as theme songs to a variety of anime series, including First Love Limited, Sora no Manimani, Demon King Daimao, Asobi ni iku yo! and Ryūgajō Nanana no Maizōkin. The group features in the anime Natsuiro Kiseki, in which every member has a role as the four main characters.