I've been trying to find this anime for years, the last time I saw it was in 2002 when I was 4. I remember it was on a VHS that we rented.
It was about a red-haired boy, who I believe fought demons. He would transform in the style of Yugi Muto into a bigger and older-looking self when fighting those demons.
I can only remember one episode where he fought a super fast wolf-looking demon that was actually a young marathon runner possessed by some king of a golden eye if I remember correctly. Anyway, the red-haired boy protagonist would eat that eye when he defeats his opponent and they would return to normal.
That's about all I can remember, and I would appreciate all the info I can get, thanks.