Here is the full list of all 78 Within the Blade achievements.
Seppuku
Complete the first mission
First kill
100 kills
500 kills
Behead 100 enemies
Behead 500 enemies
Assassination
Assassinate 50 enemies
Assassinate 250 enemies
Assassinate 500 enemies
Kill first boss
Craft anything
Guess the recipe
Make a purchase
Kill 15 heavy samurai
Kill 50 heavy samurai
Kill 100 heavy samurai
Collect 500 coins
Collect 1000 coins
Collect 5000 coins
Kill Shutendoji
Assassinate 10000 enemies
Kill by shurikens
50 kills by shurikens
250 kills by shurikens
Kill by explosions
50 kills by explosions
100 kills by explosions
Make 100 diagonal cuts
Make 500 diagonal cuts
Make 100 horizontal cuts
Make 500 horizontal cuts
Кusarigama kill
50 kusarigama kills
150 kusarigama kills
Murder in melee
50 murders in the melee
250 murders in the melee
500 murders in the melee
Kill by poison
Kill by fire
Break the Sword
Pull the enemy with the hook
Learn all skills in the hand-to-hand combat
Learn all skills in the Shurikenjutsu techniques
Learn all skills in the Kusarigama combat
Learn all the skills of the blacksmith
Learn all skills in the Shinobigatana combat
Destroy 200 boxes
Kill Gashadokuro
Kill Asura
Kill Jorogumo
Kill Tabiakindo
Kill Tengu
Kill Fudo
Kill Oni
Kill Mamoru
Complete the game (permadeath mode)
Complete challenge
Complete all challenges
Complete all tasks in 1 act
Restore the village
Complete all tasks in 2 act
Complete all tasks in 3 act
Complete all tasks in 4 act
Find all coins in challenges
Kill an enemy with skill
Block 10 Shuriken or Arrows