3x3 Eyes: Seima Densetsu

Mystical girl with amnesia is found by her immortal guardian servant (who also happens to be a love interest). 

They're both pretty short OVAs packed with action and magic. They incorporate mythology and philosophy with a bit of a twist (the second 3x3 OVA has more of these elements than the first). Unforeseen twists at the end in both shows. 3x3 Eyes has a better fleshed out story, more character investment & action (also gore). Shamanic Princess has a dreamier, art nouveau-esque style and a greater focus on magic. There is a romantic core around which both stories evolve. This is a more innocent love in 3x3 Eyes complicated by circumstance and a more mature, grown-up sort of love in Shamanic Princess. There is a bittersweet element to both shows' romantic arcs. read more 

Old time Anime done in with a dark, Gothic animation style that is never used anymore, and the plot deals with the end of the world scenarios involving monsters.