Here is the full list of all 26 √Letter - there are Root Letter - there are achievements.
All routes completed.
Finish The Bond of Marriage Chapter 10.
Finish The Bond of Marriage Chapter 9.
Select all letter replies.
Complete the Cursed Letter Route, Princess of Himegamori Forest Route, A Government Plot Route, and Crossing Paths Route.
Finish A Government Plot Chapter 10.
Finish A Government Plot Chapter 9.
Acquired all items.
Finish The Princess of Himegamori Forest Chapter 10.
Finish The Princess of Himegamori Forest Chapter 9.
Finish Crossing Paths Chapter 10.
Finish Crossing Paths Chapter 9.
Spot SHIMANEKKO 10+ times.
Finish The Cursed Letter Chapter 10.
Finish The Cursed Letter Chapter 9.
Finish Chapter 8.
Finish Chapter 7.
Finish Chapter 6.
Finish Chapter 5.
Use the "Check" command 200+ times.
Finish Chapter 4.
Finish Chapter 3.
Finish Chapter 2.
Use the "Check" command 100+ times.
Finish Chapter 1.
First conversation with SHIMANEKKO.