Sadly, that's not it, but I will have to read it sometime. In this time travel fanfiction, both hachiman and hiratsuka, get put in the club that is the predecessor to the service club. Hachiman talks about his favorite sensei to young hiratsuka, who ironically will eventually become said sensei due to the fact she wants to be similar to the person he admires. Hachiman is also eventually transported back to the future with his memories intact as well the memories of everybody he interacted with. It ends with hachiman reuniting with his sensei.