Filia, also spelled at some points in the game as Philia, is a minor character in Witch Spring 3. If you never enter the Red Fox Forest, where she lives, or don't explore the area much, it is possible to never encounter her.
The first time Eirudy encounters her, she appears to be a strange-looking fox in the Red Fox Forest. When Eirudy approaches her hiding spot, she runs away.
The second time Eirudy enters the Red Fox Forest, and goes to the back left-hand corner of the map, she will notice a teleport circle much like the one at Wardilum. There, she sees the "strange fox" again and identifies her as a deity. Filia, surprised that she was found out, stands up to reveal herself.
It seems that Filia uses vines in battle, which are capable of restraining her opponents.