oh, wow, #1 fic as intro to a new fandom...? it depends on what genre they like I suppose, but I think it might be Every Version of my Name by Mindelanwolf: https://archiveofourown.org/works/33805891. This fic is just laugh out loud funny and tender and perfectly encapsulated. A good length for a fulfilling meal while not being intimidating. 3ra forever also <3