The following is a list of ALL the secret achievements and what has to be done to get them.

Indomitable Spirit (5)
Chose to continue the game 100 times.

One Of White (15)
Purified the site of the the 1st Test of Valor.

Two Of Black (15)
Purified the site of the the 2nd Test of Valor.

Three Of Blue (15)
Purified the site of the the 3rd Test of Valor.

Four Of Green (15)
Purified the site of the the 4th Test of Valor.

Five Of Yellow (15)
Purified the site of the the 5th Test of Valor.

Six Of White (15)
Purified the site of the the 6th Test of Valor.

Seven Of Red (15)
Purified the site of the the 7th Test of Valor.

Eight Of White (15)
Purified the site of the the 8th Test of Valor.

Nine Of Violet (15)
Purified the site of the the 9th Test of Valor.

Completed Chapter 1 (10)
Finished Chapter 1 - 'Sky City Tokyo'.

Completed Chapter 2 (10)
Finished Chapter 2 - 'The Castle of the Dragon'.

Completed Chapter 3 (10)
Finished Chapter 3 - 'Thunderclap of Catastrophe'.

Completed Chapter 5 (10)
Finished Chapter 5 - 'The Aqua Capital'.

Completed Chapter 7 (10)
Finished Chapter 7 - 'The Flying Fortress Daedalus'.

Completed Chapter 9 (10)
Finished Chapter 9 - 'Heart of Darkness'.

Extinguished The Flame (15)
Annihilated Zedonius, the Greater Fiend of Flame.

Silenced The Storm (15)
Annihilated Volf, the Greater Fiend of Storms.

Diffused The Lightening (15)
Annihilated Alexei, the Greater Fiend of Lightning.

Redeemed Genshin (15)
Freed Genshin's soul and ended the reign of the Black Spider Clan.

Staunched The Blood (15)
Annihilated Elizébet, the Greater Fiend of Blood.

Ended The Infernal Reign (15)
Annihilated the High Infernal Priest, Dagra Dai.

First Medallion (20)
Obtained a Medallion in a Survival Mission

Acolyte of Missions (20)
Completed ALL Karma Attack Missions on 'Path of the Acolyte'.

Warrior of Missions (20)
Completed ALL Karma Attack Missions on 'Path of the Warrior'.

Mentor of Missions (20)
Completed ALL Karma Attack Missions on 'Path of the Mentor'.

Master Ninja of Missions (20)
Completed ALL Karma Attack Missions on 'Path of the Master Ninja'.

Four Missions Completed (30)
Completed 4 Missions

Eight Missions Completed (30)
Completed 8 Missions

ALL Bronze (30)
Obtained ALL Bronze Medallions in the Survival Missions

ALL Silver (30)
Obtained ALL Silver Medallions in the Survival Missions

ALL Gold (30)
Obtained ALL Gold Medallions in the Survival Missions

Here are ALL the achievements and what needs to be done to get them.

Mastered Reverse Wind (5)
Successfully perform the Reverse Wind technique.

Mastered Furious Wind (5)
Successfully perform the Furious Wind technique.

Mastered Shadowless Footsteps (5)
Successfully perform the Shadowless Footsteps technique.

Mastered Flying Swallow (5)
Successfully perform the Flying Swallow technique.

Mastered Flying Bird Flip (5)
Successfully perform the Flying Bird Flip technique.

Mastered Obliteration Technique (5)
Successfully perform the Obliteration Technique.

Mastered Ultimate Technique (5)
Successfully perform the Ultimate Technique.

Mastered Ultimate Guidance (5)
Successfully perform the Ultimate Guidance technique.

Mastered Counter Attack (5)
Successfully perform the Counter Attack technique.

Mastered Unrivaled Soaring (5)
Successfully perform the Unrivaled Soaring technique.

Mastered Invisible Path (5)
Successfully perform the Invisible Path technique.

The Art of the Inferno (5)
Successfully perform the Art of the Inferno Ninpo.

The Art of the Wind Blades (5)
Successfully perform the Art of the Wind Blades Ninpo.

The Art of the Flame Phoenix (5)
Successfully perform the Art of the Flame Phoenix Ninpo.

The Art of the Piercing Void (5)
Successfully perform the Art of the Piercing Void Ninpo.

Dragon Sword Master (5)
Complete the game using only the Dragon Sword.

Lunar Staff Master (5)
Complete the game using only the Lunar Staff.

Falcon's Talons Master (5)
Complete the game using only the Falcon's Talons.

Dual Katana Master (5)
Complete the game using only the Dragon's Claw and Tiger's Fang.

Kusari-gama Master (5)
Complete the game using only the Kusari-gama.

Eclipse Scythe Master (5)
Complete the game using only the Eclipse Scythe.

Tonfa Master (5)
Complete the game using only the Tonfa.

Vigoorian Flail Master (5)
Complete the game using only the Vigoorian Flail.

Vanquished Alexei (15)
Defeat Alexei in battle.

Vanquished Volf (15)
Defeat Volf in battle.

Vanquished Zedonius (15)
Defeat Zedonius in battle.

Vanquished Elizébet (15)
Defeat Elizébet in battle.

Vanquished Genshin (15)
Defeat Genshin in battle.

Karma of the Warrior (20)
Obtain 10 Crystal Skulls.

Karma of the Mentor (20)
Obtain 20 Crystal Skulls.

Karma of the Master Ninja (20)
Obtain ALL of the Crystal Skulls.

Feat of a Hundred Slashes (20)
Achieve a 100-hit combo with any weapon.

Feat of a Thousand Obliterations (20)
Defeat 1000 enemies using Obliteration Techniques.

Feat of Ultimate Destruction (20)
Defeat 1000 enemies using Ultimate Techniques.

Way of the Acolyte (100)
Complete the game on the Path of the Acolyte.

Way of the Warrior (100)
Complete the game on the Path of the Warrior.

Way of the Mentor (100)
Complete the game on the Path of the Mentor.

Way of the Master Ninja (100)
Complete the game on the Path of the Master Ninja.

These bonus features become unlocked when you complete the corresponding task in the game on the indicated setting.

Unlock Black Jaguar Costume:
Complete Path of Mentor mode.

Unlock Camoflauge Ninja Costume:
Complete the game on Warrior mode.

Unlock Red Ninja Costume:
Complete the game on Acolyte mode.

Unlock Golden Ninja Costume:
Complete the game on Path of The Master Ninja mode.

Unlock Music Test:
On any difficulty setting beat the game.

Unlock Old Film Filter:
On any difficulty setting beat the game.

Unlock Gamerpic;
Collect ALL 30 crystal skulls.

When you complete the game on the indicated setting the corresponding mode will become an available option.

Unlock Survival Challenge Mode:
Complete the game.

Unlock 'Path Of The Mentor' Mode:
Complete the game on the 'Path Of The Warrior' difficulty.

Unlock 'Path Of The Master Ninja' Mode:
Complete the game on the 'Path Of The Warrior' difficulty.

When you have completed the game on any difficulty setting and saved it when you are prompted you will retain ALL weapons, life, ninpo, items and essence you had in that game when you begin a new game on the same difficulty setting using that saved file.