The protagonist discovers that his grandfather's shop is actually the "Yin Yang Station" and the daily necessities are express delivery to "over there"
Gold Finger Upgrade: The paper objects you stick out can be "sent" to the underworld and can also be "received" from the underworld.
Main line: Investigate the turmoil "over there" - the city god system collapsed, and evil ghosts took advantage of the chaos to sneak into the underworld.
