Ai Space (悠幻影(アイ・スペース) ai supesu; Japanese for "Eternal Illusion") is the Magical Dimension where only Magi can enter.
Ai Space is a parallel dimension created by Odin to hold the ritual known as Ragnarök. It draws only people who can use magical armaments, in other words: magi, inside and will obliterate everyone, except Odin himself, unless one is sacrificed within 12 hours. The field will automatically return the magi to the real world once a sacrifice has been made, but Odin can call forth Ai Space again whenever he wants. Jin Arizuka also can make Ai Space occur, since he is the Game Master, but his control over the field is seemingly more limited.
It is later revealed that the origins of Ai Space dates back to 14 years ago. According to Ichigo Sagara, Ai Space was created during the war by Voluspa to minimize damage to by Magi to the surface. The field was originally generated by a machine incorporated with O Parts and is said to be only barely resembles the Ai Space created by Odin. The machine was destroyed by the magi "Rouge Flame" in the "Fimbulvinter War" and reduce to smals pieces of scrap metal. (Ichigo explained to Reiji that the machine was enormous before it was destroyed).