This is actually the cover for a doujin game being developed by Frontier Aja ( http://aja-games.com/ ) called 紅魔城伝説 スカーレット・シンフォニー (Roughly translated: Legend of the Crimson Devil Castle: Scarlet Symphony). There are screenshots on the web site, it looks pretty good. The site mentions that they plan on releasing it at the summer comiket.