if he controls anyone who steps on his shadow, why does he step on the shadow of everyone else instead? Use the damn skill if you are giving us exposition on it!
@feha Goodknife explained it below. It's clearly supposed to be "I can control [dominate/freeze up] anyone by stepping on their shadow", expecially if you look at the scene where he did use his skill successfully.
@Simpleton nah, thats not what ninja said. He is clearly avoiding using his skill, people can even speak when he steps on their shadow instead of vice-versa
he still kept his like for stepping on others shadows for no reason, but somehow came up with a solution to lock her movements despite that. Maybe the demons skill affected more than her shadow being a gate?
Although if I look closely, odds are he isn't stepping on her shadow, as she has a shadow in opposite dir too. So more likely he avoided the gate even if it was sealed, and decided to approach with sun at his back to force her onto his own shadow. So he fixed his habit.