Here is the full list of all 10 Fujiwara Bittersweet achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
You finished all the routes
You finished at least one "Sweet Route"
You picked Ryu's route
You picked Kenji's route
You picked Haru's route
You picked Yuta's route
You picked Toshio's route
You finished at least one "Friend Route"
You picked Ikki's route
Start a new game