our Ni or "Star" will be lined up on the #2 receiver. The #3 could be a TE or a RB and the MIKE relates to that guy
the CBs have the #1 guys ...

so a slot's assignment in many schemes will be one of three things --- in this case if the route breaks out
the Ni takes him man to man.

if the goes deep --- Ni takes him man to man

But if the #2 cuts inside he delivers him to the MIKE and would trail or stay at home to help when the next guy comes through
could be the #3 going out or the #1 coming in.