By clearing the Arcade mode (Acceleration of SUGURI and X-Edition) without using any continues, you can unlock an Extra story for certain characters of the game. The Extra stories can only be unlocked for Suguri, Saki, Iru, Nanako, Kae, Kyoko and Sora.

Unlockable	How to unlock
Extra Story for Iru	Clear Arcade mode as Saki without using a continue.
Extra Story for Kae	Clear Arcade mode as Kae without using a continue.
Extra Story for Kyoko	Clear Arcade mode as Kyoko without using a continue.
Extra Story for Nanako	Clear Arcade mode as Nanako without using a continue.
Extra Story for Saki	Clear Arcade mode as Iru without using a continue.
Extra Story for Sora	Clear Arcade mode as Sora without using a continue.
Extra Story for Suguri	Clear Arcade mode as Suguri without using a continue.