The OVA Strong World 0, is a great one to start out with, before going for the movie. The OVA starts out with kinda few spoilers, where we get to see the end of the Strong World movie. Personally, I would skip it as you basically will kinda figure out what will happens in the movie 0:00-1:45 ish skip that, if you don't want to see, the ending of the Strong World movie. other than that we get a quick great recap of who Shiki is and what he really is. we see a lot of characters as young that is quite cool aswell.

Overall great OVA with a rather great ending that opens up your curiosity.