In Engpsh, you can describe a person who is a very passionate and enthusiastic fan as "crazy" or "wild" about something. For example, you might say "She's a crazy fan of that band," or "He's wild about basketball." You can also use the phrase "obsessed fan" to describe someone who is very passionate and focused on a particular thing or person. For example, you might say "He's an obsessed fan of that author," or "She's a huge fan of that TV show, she's completely obsessed."