Feel like Suzu's a little off the mark re: Shinonome making it so spirits can move up and down stages.
I think she got them down to stage zero when she first recruited them and then somewhere during the process of living in the apartment and having jobs and friends they moved to a new stage where they're way more human like and can emote normally.
Such that Kamikiri isn't switching between stage zero and stage 1 when he smiles, he's just happy.