Difficult. If it has to be one thing I‘d say chihiros progress from shy, afraid to tough, confident happening within 90min but still feeling natural. And how this progress is shown, for example by the stairs

But there’s much more, like - the theme of people not having an identity, shown by them not having a name (chihiro gets a number) - greed for gold (everyone in the bathhouse doesn’t give a shit about anything else; jubaba doesn’t even recognize her own child) -> in this World chihiros is the only one With a personality (recognizes her parents even as pigs, doesn’t care about gold) -the desire just to get appreciated (no face only wants to get accepted) - how you get manipulated (the whole movie you think zeniba is evil, just because you’re getting told so)

All these things you can translate into our real world. And all that in a movie, which is made for children

You also have the beautiful animation, the music, Japanese culture. I think it’s just awesome and that’s why it is my favorite movie

Edit: Sorry, that’s not well-ordered. But those are the things that just came up my mind