Busou Shoujo Machiavellianism OVA
Bundled with the limited edition 7th volume of the Busou Shoujo Machiavellianism manga.
Disappointed by how all members of the Supreme Five Swords were single-handedly taken out by the Empress, the headmistress ordered the Five Swords to a recreational trip to strengthen their bonds. Apparently, there are some extra budget to accommodate an extra sixth person on the trip. Both Rin and Mary wanted Nomura to be sixth person, but there may be some hurdles on making that a reality.
(Source: Muse Asia)