Onimusha: Way of the Sword

Carnage difficulty:
Complete the story once to unlock the Carnage difficulty (played in New Game+).

Unlockable outfits:
Outfit                       How to unlock
Tasuki Sash                  Complete the mission "The Stage is Set at Kiyomizu"
Wataru-kun Costume           Complete the main story (unlocked after the credits)
Panda Costume                Complete the main story on any normal difficulty
Master Outfit                Complete the main story on any normal difficulty
General Armor / Warrior's Great Armor   Defeat all the Practice Grounds bosses on Story or Action difficulty
Light Kimono 2               Complete "The Stage is Set at Kiyomizu" on Carnage
Carnage Story Outfit         Complete the entire story on Carnage
Carnage Rematch Outfit       Defeat the complete Boss Rematch roster on Carnage

Lion Dog sword skins:
Rescue Lady Murasaki's 36 Lion Dogs (the collection opens after the mission "What Lurks in the Shadows") and report back to her at Yasaka Shrine.
Sakurahime     6 Lion Dogs
Shishioh       12 Lion Dogs
Myogo          18 Lion Dogs
Ura-giri       24 Lion Dogs
Mooncrossed    30 Lion Dogs
Kikoku         All 36 Lion Dogs

Note: Sword skins are cosmetic only and do not change damage or speed. Some skins and outfits (e.g. Red Armor, Sealed Curse, White Lion) are only available as pre-order or Deluxe edition bonuses.