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