Here is the full list of all 55 Onimusha: Warlords achievements.
Enter the abandoned keep.
Obtain the Kouen.
Defeat Osric.
Save a soldier under attack by demons.
Win a power struggle with a demon.
Enhance equipment at Magic Mirror.
Obtain the Shiden.
Use a Special Attack to kill a demon.
Use the gauntlet to absorb demon souls.
Obtain the Arashi.
Defeat Marcellus.
Defeat Stylado.
Defeat Barabazuu.
Defeat Hecuba.
Defeat Marcellus's final form.
Defeat Fortinbras.
Solve the crest puzzle.
Unseal the path to the Keep Underground.
Obtain the Sacred Knife.
Use the Decorated Sword to enter the East Area.
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 Vision Staff.
Obtain all long-range weapons.
Obtain all armor for Samanosuke.
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.
Enhance all orbs 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.
Kill a demon with a battering ram.
Solve all number puzzles.
Solve all decoder boxes.
Obtain the Rosary of Communication.
Spot the flock of wild geese at dusk.
Find the beetle on the tree trunk.
Absorb souls from carp.
Cut down bamboo in the bamboo forest.
Speak to the first and second old moth man.