Image description- digital art of Kai and Sei posed from the waist up together in front of a plain wall with a single brown strip like they're having a picture taken together. Sei is doing "bunny ears" behind Kai's ear. Sei is wearing a happy smile, Kai has an midly annoyed expression. Besides Kai there is an "..." while sei has two little lines besides him
As I understand, trick-or-treating isn't very popular in Japan. However, I imagine that once little Sou would learn of this Western tradition, he'd be very eager to try it out (for once, he gets to scare people AND get candy for it). So Momdori would alert the neighbors of her son's intentions, then pressure Gashu to dress up his own kids to keep Sou company. I think, Sei wouldn't mind (he'd eat Sou's candy when he's not looking though), whereas Kai would be quite embarrassed by this experience.