This game is titled Half-Minute Hero in North America and Europe, and Yuusha 30 in Japan.
Hero 300 mode
Successfully complete Knight 30 mode.
Hero 3 mode
Successfully complete Hero 300 mode.
Knight 30 mode
Successfully complete Hero 30, Demon King 30, and Princess 30 modes.
Successfully complete Hero 3 mode. Press Select to access the music player.
Strategy guides from GameFAQs