Strike the Blood: Valkyria no Oukoku-hen
Strike the Blood OVA
Strike the Blood: Kingdom of the Valkyria
It was officially announced at the Dengeki Game Festival 2015 event that Strike the Blood will be getting a two-episode OVA series to be released at the end of 2015. The OVA will be an original story written by Gakuto Mikumo.
(Source: MAL News)