This Achievement is to use all the Soul Breaks in the Game. Each character has 3-4 Soul Breaks which are for the most part unlocked via levveling up however the final Soul Break for each character is locked in the final dungeon with their 3rd Mystic Art. In the final Dungeon you will come across 6 orbs, collect them and put them into the correct stand to unlock a warp point that takes you to a Boss. Defeat that boss and you will earn a Mystic Art and Soul Break for a specific Character
Red – Laphicet
Yellow - Eizen
Blue - Eleanor
Green - Rokurou
White – Magilou
Violet - Velvet
They are not difficult to find but make sure you explore all the warp points and keep not of where the orb monoliths are.
Velvet
Consuming Claw - Hold R key or RT with three or more souls to activate this Soul Break
Heaven's Claw - Hold R key or RT while in Therion mode with 3 or more souls after making a successful hit
Hell's Claw - Hold R key or RT while in Therion mode with 3 or more souls after making a two hit combo
Nightmare Claw - Hold R key or RT after a 3 hit combo and being in Therion Mode for 20 seconds.
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Laphicet
Divide Pain - With 3 or more souls, hold the R key or RT Button
Static Force - With 3 or mour souls, hold the R key or RT button while in Divide Pain
Soul Distortion - With 3 or mour souls, hold the R key or RT button while in Static Force
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Eizen
Draconic Drive - With 3 or more souls, hold the R key or RT Button
Dragon Dive - With 3 or mour souls, hold the R key or RT button while in Draconic Drive
Tyrant's Fete - With 3 or mour souls, hold the R key or RT button while in Dragon Dive
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Eleanor
Aerial Strike - With 3 or more souls, hold the R key or RT Button
Strike Zwei - With 3 or mour souls, hold the R key or RT button while in Aerial Strike
Strike Drei - With 3 or mour souls, hold the R key or RT button while in Strike Zwei
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Magilou
Spell Absorber - Hold R key or RT with three or more souls to activate this Soul Break
Calamity Flare - Automatically activates when Spell Absorber absorbs enough enemy arts
Violent Storm - Automatically activates when Spell Absorber absorbs enough enemy arts
Flare Vortex - Automatically activates when Spell Absorber absorbs enough enemy arts
Hydrostorm - Automatically activates when Spell Absorber absorbs enough enemy arts
Gravity Gale - Automatically activates when Spell Absorber absorbs enough enemy arts
Lightning Blast - Automatically activates when Spell Absorber absorbs enough enemy arts
Tetra Detonator - Automatically activates when Spell Absorber absorbs enough enemy arts
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Rokurou
Vengeful Stance - With 3 or more souls, hold the R key or RT Button to enter a parry stance and increases Stun rate
Vengeful Punishment - Automatically activates when hit while in Vengeful Stance and delivers a powerful counter
Vengeful Scourge - A powerful counter attack that executes after performing a combo with Vengeful Punishment without taking damage
Vengeful Retribution - Hold the R key or RT with 3 or more souls while in Vengeful Scrouge
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Setup
Eizen, Laphicet and Eleanor are easily done via the Slash Beat Mini-Game. Simply load it up with the appropriate character, stun the dummy twice so you have 5 souls and Hold R key or RT until all the Soul Breaks activate.
Magilou can be done via the Undead Quarter Class 4 Area. Set the strategy for all the characters to defend only. Equip your weakest equipment if you are too strong. All you need to do is activate Spell Absorber with the R key or RT while enemies are buffering spells (Diamond icon that has line go around it). There will be a bar that fills up at the bottom. Each Break Soul activates in stages, so when you use it, it will activate one of the the listed break souls automatically. The next time you use it, a different spell will activate and it will go through the list until all of them have been used and then it will start from the 1st spell again. Each spell has a high chance to stun so you shouldnt have to worry about Souls.
Velvet is a tricky one. First 3 are pretty simple and can be done in the Slash Beat Mini-Game. However the 4th one is a pain in the butt as you need to be in Therion mode for 20 seconds. This is best done against tough enemies that wont die easily. Initiate Consume Claw and keep yourself active but dont use the combo finisher. Attack 2 or 3 times then run away. Try to keep count of how long you have been in Therion Mode. I typically used the R key or RT in Therion mode approx every 10 seconds as I found that the finisher would automatically initiate on its own if I didnt. After 20 seconds is up, hold the R key or RT to initiate Nightmare Claw. Since this one could give you trouble I suggest doing the Mystic art at the same time for the Witness to the mystic. Make sure you have 5 BG to do it.
Rokurou is another tricky one. I recommend using the Armor Quarter Class 4 Zone. Use the same setup as with Magilou. Put everyone in Defense only and equip your weakest stuff if you are too strong. This on is tricky because due to understanding how his break soul actually works. His first break soul is just the stance which kind of threw me off. When he disappears and appears behind the enemy and uses an attack that is his second break soul which happens automatically as the enemy attacks you in his parry stance. After that just keep attacking and keep an eye on the top of the screen where you see the arts. If you complete a combo without being hit right after the 2 break souls the 3rd one should pop up (Vengeful Scourge) there and initiate automatically and then you can hold the R key or RT to use the 4th break soul. At that time you might as well use the Mystic art as well by holding LT while in Vengeful Retribution for the Witness to the Mystic Achievement. It requires 5 BG to do.