What kind of title is this?: Manga.
Where can I read it?: Reading links are listed for Official Site, Seven Seas Entertainment, Pixiv Comic. Check availability in your region.

Synopsis

About A Tale of the Secret Saint

Born into a family of knights, Fia has always dreamed of following the path to knighthood too, except she’s the least talented of them all. On the day of her initiation test, a deadly injury prompts her life to flash before her eyes…and reveal her former life as a powerful Saint who defeated the Demon King in a bygone era! Her painful death as a Saint made her swear she’d never accept sainthood and its dangers again. But now, with her saintly power returned, Fia has the chance to be a more powerful knight than she’d ever dreamed—that is, if she can last long enough (Source: Seven Seas Entertainment)

Action Adventure Fantasy