Perhaps the direction of the story was hastily written by fate at the moment they met.
Some people are destined to stay in the summer of eighteen, some people spend the rest of their lives to atone for their youth, and some people are gray-haired and forget all the past, only remembering to hold old things and remember old people.
*Don't ask, just ask, please forgive me for the poor writing!
Concept: "In this world, there are unexpected encounters and unexpected goodbyes."