An accident occuring in “The World”, will be solved in the net framework space, with the OVA “Liminality”. Mai and Kasumi collapse in the real world, however, only Mai recovers, leaving Tomonari in a coma. The incident will be investigated through the real world point of view. You will continue to come closer to the truth of the accident within the game while investigating from the real world in the OVA.
Descriptions taken from AniDB.net