The island in the anime
Kamikura Island (神座島, Kamikura-jima) was discovered in 1999 by Minaka Hiroto and Takami Sahashi who stated that this island is a geologically impossible formation. The island suddenly appeared in an area in the seas off Japan. On this island, they later discovered the giant alien ship with 108 lifeforms, the Sekirei inside[1].
Some time later, after the founding of MBI, Kamikura Island was turned somehow by Hiroto Minaka into private land, removed from the maps and it became an extraterritoriality[1]. Now the authorities of the world reacted and started the invasion of Kamikura Island of which the first attack wave was the strongest and most aggressive. The newly formed Disciplinary Squad's first generation was able to withstand all three attack waves of the attacking international army and was able to protect the still sleeping 103 Sekirei[2]. All Sekirei were raised, adjusted and grew up on this island before they were released in the outside world to find their Ashikabi[3].
Since its discovery, Kamikura Island has undergone a number of attacks. The second generation Disciplinary Squad consisting of Yume and Karasuba repetitively defended the island successfully[4].
The final known attack takes place during the final stage of festival of the sekirei plan after Ashikabi Hayato Mikogami and Sekirei Mutsu 'break' the ship contained within to escape Akitsu's norito[5] in effect causing Minaka Hiroto to loose contact with MBI.