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Fanon keeps making Sirius the one who looks up to James, and I agree with that to an extent, but I think James was the one looking up to Sirius most of the time (James stopped playing with the snitch for Sirius when he wouldn’t for anyone else; you don’t do that if you don’t look up to someone!).
Imagine James who sees Sirius’ many, many piercings and, even though he’s scared of needles, gets his lobes pierced. Imagine James who sees Sirius’ tattoos and gets a little paw print on the inside of his wrist. Imagine James who sees Sirius’ quick wit and sharp tongue and tries to emulate it whenever people are mean to his friends. Imagine James who sees Sirius leaving his tie undone and starts doing that, himself. Imagine James who sees Sirius and wants to be like him, so effortlessly cool and funny and handsome.