I didn't really like that one, it's like our fourth 'It can control everyone' monster.
It doesn't actually control people. The daily grind is considered necessary. It only "controls" people like hunger does by making you eat. You need to go get food from the supermarket. In Japan they usually do that daily.
The only supernatural aspects in this story, which only affect this particular store, are these:
The mystery man makes people see their daily repetition (which in Japan necessarily involves the supermarket) as a cage, as a hell they want to escape from. It targets those who are already tired of it and amps up their feelings.
The supermarket wants people to continue the daily grind. It sort of embodies it. Work and chores and such also involve the daily grind, but people don't all work and live in the same places, and the experiences are different for each person. The supermarket is the common aspect of the daily grind.
People who have been influenced by the mystery man are killed. Either by the mystery man himself to free them, or by the supermarket for getting close to him.
My guess is the supermarket. We see the mystery man, and then people know to look for a corpse. However, apparently you can become the mystery man. So what if the corpses come first, the person having been killed by the supermarket for realizing the "truth", they turn into a mystery man, who is then spotted. Maybe the inner line 9 thing is to pacify the supermarket, not the mystery man.
But anyway, yeah, this doesn't control everyone even just at this location, and certainly not anyone anywhere else.