After defeating the various Floor Masters of the six prior levels, Hakuno Kishinami and Saber arrive at the top floor of the Moon Cell. Their opponent will be Leonardo B. Harwey—the strongest Master in the history of the Holy Grail War and the current fan favorite, following his previous victory. As they reach a field of flowers among floating isles, Hakuno, Saber, and Rin Toosaka come across a hooded man tending to the blossoms. Saber immediately draws her blade before the cloaked figure, who reveals himself as Prince Gawain: the Platinum Saber and Knight of the Round Table. However, when Gawain insists that he has no interest in fighting, the four discuss the infinite possibilities for the Holy Grail, with Hakuno determined to return the Moon Cell to its original form. Their discussion ends with a clangor from afar, ringing through the skies. The threadbare Gawain, knowing its significance, informs the three that not much time remains for their lives. He beckons them towards the final battleground, where the two Sabers shall duel once more to determine the future of mankind. [Written by MAL Rewrite]

Recaps of ONA (Episode 0) and 2013 TV Anime Series (Episode 10.5).

On the "Spooner Continent", a valiant group of Sorcerer Hunters are the people's last line of defense against the evil dark magiks unleashed periodically by those who can't control it. Saving the world and looking sexy while doing it! (Source: AniDB)

Mini OVA episodes bundled with the Blu-ray and DVD releases of Valkyrie Drive: Mermaid.