Hatsuki is a highschool student living with her sister, Hatsumi, who she has a huge crush on. On Hatsumi's 16th birthday, she is suddenly surrounded by a green light and disappears in front of Hatsuki. She manages to follow Hatsumi with the help of a being resembling a fat baby chick (literally), ending up in a place called "The Great Library", which is full of different worlds stored in books. Hatsumi wasn't there, though, so the search for Hatsuki's great love begins and involves traveling from book to book. (Source: AniDB)

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)