According to Kodansha, two OVAs of Sankarea
were announced to be bundled with the six and seventh volumes of the comic books. The first and second volumes will be released on June 8th and November 9th. The story of the first volume is an original one written by the manga's author. Before the beginning of the main story, Rea and Chihiro have already encountered at a certain place—an outdoor hot-spring bath.
Source: Sankarea OVA official website