Autistic son obsessed with anime character Sakura haruno

So recently my eldest son has been interested in anime including naruto and my hero academia. He had recently become obsessed with the naruto character Sakura Haruno. He's been watching videos and cosplays of her online, searching things up about her and keeps talking about her to me. He now also wants to cosplay as her. 

Does anybody know how to tell him to calm down about his obsession without offending him.