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