Here is the full list of all 55 Onimusha: Warlords achievements.
Defeat Hecuba.
Solve all number puzzles.
Solve all decoder boxes.
Obtain all armor for Samanosuke.
Use the Decorated Sword to enter the East Area.
Enhance all orbs to maximum.
Obtain all long-range weapons.
Kill a demon with a battering ram.
Obtain the Vision Staff.
Defeat Stylado.
Obtain the Sacred Knife.
Cut down bamboo in the bamboo forest.
Speak to the first and second old moth man.
Obtain the Rosary of Communication.
Unseal the path to the Keep Underground.
Obtain the Arashi.
Defeat Marcellus.
Solve the crest puzzle.
Enter the abandoned keep.
Obtain the Kouen.
Defeat Osric.
Enhance equipment at Magic Mirror.
Save a soldier under attack by demons.
Obtain the Shiden.
Use a Special Attack to kill a demon.
Use the gauntlet to absorb demon souls.
Defeat Barabazuu.
Defeat Marcellus's final form.
Defeat Fortinbras.
Open the gate to the Demon World.
Complete the first half of the Dark Realm.
Complete the second half of the Dark Realm.
Complete the game on Normal without enhancing swords or using Jewels.
Complete the game on Ultimate difficulty.
Complete the game on Normal without using herbs or medicine.
Complete the game in less than 3 hours.
Complete the game and get an S Rank.
Complete all stages of Oni Spirits.
Obtain the Bishamon Sword.
Collect all files.
Collect all maps.
Collect all Fluorite.
Unlock Samanosuke's alternate outfit.
Unlock Kaede's alternate outfit.
Enhance the gauntlet to maximum.
Enhance all swords to maximum.
Use Power Jewels to increase Vitality to maximum.
NEW_ACHIEVEMENUse Magic Jewels to increase Magic Power to maximum._DESC_2_7
Strike a demon with Kaede's Special Attack.
Strike Marcellus's final form with a Deflect Critical attack.
Defeat a demon by knocking it down the waterfall.
Win a power struggle with a demon.
Spot the flock of wild geese at dusk.
Find the beetle on the tree trunk.
Absorb souls from carp.