While you can start directly with the main manga, fans often suggest this order to understand the full lore:

What order do I read the Owari no Seraph manga? : r/OwarinoSeraph

: Dark fantasy, action, and post-apocalyptic themes centered on a war between humans and vampires.

: While there isn't a single "paper" book containing the entire run due to its length (currently ongoing at 155+ chapters), you can purchase complete sets from retailers like eBay or local bookstores. Recommended Reading Order