Flora is Schierke's mentor and teacher in magic and Od—the spiritual energy that flows through all living things. She's a powerful witch whose exact age remains a mystery, and she has history with the Skull Knight going back further than his current skeletal form; she considers him "still human at heart," which tells you something about who he used to be.
She wasn't always hidden away. Flora spent years traveling and using her magic to help people until the Holy See's growing power forced her into isolation. Now she lives in the woods near Enoch village, but she hasn't completely cut herself off from the world—the Skull Knight still calls on her when he needs her.
When Guts and his crew came through, Flora stepped in at the Skull Knight's request. She placed magical seals on both Guts and Casca's brands to keep vengeful spirits at bay, which turned out to be crucial for their survival. She also hooked them up with magical gear they desperately needed for their encounter with the trolls.
As for Guts specifically, Flora told Schierke that his fate and Schierke's are bound together—though Schierke was skeptical about it at first.
Content compiled by AnimeList.moe from publicly available sources.
