i love john's birthday letters SO MUCH. its so clear that he loves his friends and they love him back so much that they incorporate his gifts into their sense of self.
rose's strife specibus is based on the knitting stuff he got her, and dave's most iconic feature (shades) was also a gift from john. jade's gift has some weird temporal shenanigans involved and im not to that point in my reread yet, but her shirt color and interest in gardening is from john too, back before she even knew him!!!
i think its a cool way to show how we're shaped by the relationships around us. if it werent for john, the other kids would be missing some CORE aspects that make their characters recognizable, and the reverse is probably true as well.
theyre friends your honor :')