well im forced to read the book but it turns out to be really good tbh
its like this convenience store ran by an old dude called mr. namiya but the kids in his neighborhood tend to call him mr. nayami. in japanese nayami means struggle in english and 煩惱 in chinese. somehow this old dude decided to quit the business but he continued to help people to go through and help with their struggles. people write their struggles as a letter and they put the letter in the delivery slot on the roll-up door at night and they can pick-up the reply to their letter in the milk box at the back of the convenience store on the very next day. and basically stuff happens (i don't want to give any spoilers) and letters go to and fro.
BIG SPOILER: somehow the store acts as a time machine port thingy. there is a time difference between the inside and the outside of the store so you must close the doors of the store in order to differentiate. outside the store is 32 years back in time but inside the store is the present. if ur inside the store and u receive a letter, its a letter from the past and if u reply to that letter and put it in the milk box it sends your reply to the past; and if ur from the present and u put a letter inside the delivery slot people (from the present) who are inside the store won't get the letter, cuz the letter is sent to the past. 1 hour inside the store might equal to a few days back in time. its kinda confusing when u first read it but ur gonna love it when u continue the book.