Collectible Location
Letter of the Lost
1 -Sato's Letter X:435.3, Y:645.7
2 -Hyogo's Letter X:362.6, Y:709.6
3 -Mori's Letter X:460.3, Y:766.7
4 - Ren's Letter X:379.7, Y:740.7
5 -Mogi's 1st Letter X:530.2, Y:741.7
6 - Mogi's 2nd Letter X:600.7, Y:620.9
7 -Mogi's 3rd Letter X:682.3, Y:811.2
8 -Mogi's 4th Letter X:629.6, Y:645.6
9 - Tadao's 1st Letter X:632.5, Y:601.5
10 -Tadao's 2nd Letter X:703.0, Y:575.3
11 Shinji's Letter X:798.9, Y:749.8
12 -Hayato's 1st Letter X:800.9, Y:756.1
13 - Hayato's 2nd Letter X:777.8, Y:618.8
14 -Hayato's 3rd Letter X:602.5, Y:457.5
15 -Hayato's 4th Letter X:470.8, Y:418.3
16 -Masahiro's Letter X:528.6, Y:399.8
17 -Hurk's 1st Letter X:407.8, Y:498.9
18 -Hurk's 2nd Letter X:375.0, Y:314.6
19 -Hurk's 3rd Letter X:237.4, Y:425.5
20 - Hurk's 4th Letter X:497.0, Y:501.3

Collect 6 Letters of the Lost to unlock the Japanese Tanato knife. Equip it in a shop for free and use it with the meele key (F).
Collect all 20 letters to unlock the Dead Letters achievement.