tourist to school visa Q

i currently live in japan, been here for years, but my hometown friend is looking to start language school next july. they were wanting to come early though, around april and be a tourist, before leaving and coming back

my Q is, when they leave japan, do they have to go all the way back to the home country, or could we take a korea trip and come back. also would the COE have to be sent to home country then mailed to them here? thanks