Theory (Japanese: セオリ, Seori) is a Rare Blade in Xenoblade Chronicles 2. She can grant tremendous power to her Drivers, Rex, Nia, Zeke or Mòrag, and their allies. Theory uses the ice element, wields a Chroma Katana, and acts as a Tank in battle. She moves as a skater on ice with an elegance reminiscent of a fairy, similar to Praxis, another female Blade with whom Theory shares a bond.
Theory was designed by CHOCO, who also designed Praxis and T-elos.
Theory is quite cold toward others, including her Driver, but initially has a very strong bond with Praxis, who she cares for immensely. Upon being returned to her core and reawakened, Theory becomes cold again, treating Praxis distantly until they get to know each other again. She is soft-spoken but determined toward her goals.
In contrast to Praxis' rounded, bubbly appearance, Theory is made up for sharp spears of ice and harsher lines. She has a slight build, lank pale blue hair, and one blue eye (her left is covered with a black eyepatch with an ice spear sticking out from it). She wears a black tabbard with a white crop-top, loose black trousers and bronze ornamentation. Her core crystal is V-shaped and identical to Praxis'.
Heart-to-hearts and Blade Quest
Praxis takes part in two Heart-to-hearts; "Rough Diamond" and "Sisterly Love", the former in Orl Cloudway: Fonsett between Praxis, her Driver and Theory, and the latter between Praxis, Theory and Theory's Driver at Lyta Oasis. "Rough Diamond" explores how Theory has changed and lost her bond with Praxis due to returning to her core, and "Sisterly Love" shows how they've progressed since, with Theory calling Praxis "Sis", which she swore she would never do in their first Heart-to-heart. In both, the two are looking for beautiful landscapes to see.
Crystal Clear is activated automatically upon visiting Torigoth after Chapter 5 after having heard the rumour about Core Crystal Hunters; Theory and Praxis attack the party in a theft attempt. They fail and are driven off, so the party attempt to set an ambush for them which winds up being an ambush itself. The party fight Theory, her Driver and Praxis but half-way through the battle Praxis' Driver, engaging the Ardainian army elsewhere, is killed, reverting Praxis to her Core Crystal. Theory and her Driver escape, with Theory protesting greatly at having to leave Praxis.
Once Praxis is reawakened and her Affinity Chart at level 4, Blade-Sharp Memory is activated automatically upon visiting the Royal Guard Barracks in Fonsa Myma after Chapter 7. Theory throws a note attached to a lance that narrowly misses Nia, inviting Praxis to rediscover her memories in Gormott Province. Once there she throws another lance, forcing the party to tell Praxis about Theory and her past as a mercenary. Theory throws a final lance in Nharil Central Plaza in Mor Ardain inviting Praxis to the Lost Capital Judicium where she and her Driver ambush the party in an attempt to kill Praxis' Driver to retrieve her. Praxis begs Theory not to fight and insists that she doesn't want to be a mercenary, which makes Theory's Driver instruct her to kill Praxis - Theory refuses to do this and stabs her Driver instead, killing him and returning her to her Core Crystal. Praxis promises her that they will be as close when she reawakens.
Theory and Praxis
Once both awakened, Theory and Praxis decide to do good deeds to repent for their previous lives of crime. Theory and Praxis can be activated by visiting the Commercial District in Fonsa Myma after Chapter 8, after "Rough Diamond" has been viewed. They find a pair of children missing their father, fight off mercenaries who are heckling said father, and then gather ingredients to be baked into cookies for the local children.
- Lv. 1 - Ice Slash - After throwing ice knives, attack with slashes.
- Lv. 2 - Frost Banish - Release a powerful somersault kick after three repeat attacks.
- Lv. 3 - Rebel Sister - With one slash, smash an ice pillar and attack enemies over a wide area.
- Lv. 4 - Winter's Wake - Hurl out continuous ice strikes to freeze the enemy in their tracks.
- Aerial Flashdance - Counters attacks with 200% to 400% physical damage.
- Conviction - Increases damage dealt to enemies targeting user by 25% to 50%.
- Steadfast - Boosts Break resistance by 30% to 70%.
- Ice Mastery - Lv. 3
- Focus - Lv. 3
- Nopon Wisdom - Lv. 3
- Pouch item types: Veggies, Board Games
- Pouch items: Steamed Veg Stralu (Veggies), Sparkly Snow Perfume (Cosmetics)
|Type||Name||Skill Level||Affinity Level||Effect||Prerequisite||Count||Flavor Text|
|Key Affinity Reward||1||1||Affinity Chart level 1 unlocked|
|2||2||Unlocks level 2 of the Affinity Chart||Increase Trust||50||"I think we'll get on well..."|
|3||3||Unlocks level 3 of the Affinity Chart. Affinity bond will be easier to sustain.||Increase Trust||View Heart-to-Heart "Rough Diamond" then go to Uraya's Commercial District and end the quest "Theory and Praxis"||"Big sis looked really happy..."|
|4||4||Unlocks level 4 of the Affinity Chart||Increase Trust||At Lyta Oasis, Gormott, view the Heart-to-Heart "Sisterly Love"||"The three of us will make many more memories together!"|
|5||5||Unlocks level 5 of the Affinity Chart||Increase Trust||9,800||"Maybe friendship isn't so bad..."|
|Blade Special||Ice Slash||1||1||Increases aggro drawn from Specials by 60%|
|2||2||Increases aggro drawn from Specials by 70%||Perform a Blade Combo||5||"Allow me to freeze you solid."|
|3||3||Increases aggro drawn from Specials by 80%||Use Ice Slash||11||"This was the right decision...I'm sure. The power will be mine to command."|
|4||4||Increases aggro drawn from Specials by 90%||Defeat an Indoline Star at the World Tree||4||"I will grow strong. There will be no more failure."|
|5||5||Increases aggro drawn from Specials by 100%||Use Ice Slash||13||"Stand still. This will be wonderful."|
|Frost Banish||1||1||Increases damage dealt to enemies targeting user by 60%|
|2||2||Increases damage dealt to enemies targeting user by 70%||Defeat a Gamen Grebel at Spirit Crucible Elpys||5||"I hate Gamen Grebel... No more, please..."|
|3||3||Increases damage dealt to enemies targeting user by 80%||Perform a Driver Combo (It's enough to just be present)||7||"I will not fail."|
|4||4||Increases damage dealt to enemies targeting user by 90%||Use Frost Banish||9||"You need efficiency to weaken the enemy..."|
|5||5||Increases damage dealt to enemies targeting user by 100%||Defeat Impassable Edgar in Tantal||"Impassable Edgar... It was the perfect opponent to do battle with."|
|Rebel Sister||1||1||Increases critical damage by 25%|
|2||2||Increases critical damage by 40%||Use Rebel Sister||5||"I'm improving, I think..."|
|3||3||Increases critical damage by 55%||Walk a lot||10,000||"You know...I quite enjoyed the journey."|
|4||4||Increases critical damage by 70%||Perform a Driver Combo (It's enough to just be present)||10||"I've found a way to freeze an enemy to its very core. May I?"|
|5||5||Increases critical damage by 85%||Perform a Blade Combo finisher||3||"Welcome to the world of ice. It's colder than you can imagine..."|
|Battle Skill||Aerial Flashdance||1||1||Counters attacks with 200% physical damage|
|2||2||Counters attacks with 250% physical damage||Evade an attack||5||"It's all right. Stay calm and observe the enemy closely."|
|3||3||Counters attacks with 300% physical damage||Evade an attack||7||"I think I've gotten better at dodging. Let me help you."|
|4||4||Counters attacks with 350% physical damage||Evade an attack||9||"Dodge and then strike. There's only a small window of opportunity."|
|5||5||Counters attacks with 400% physical damage||Evade an attack||10||"Are you aiming for a counter?"|
|Conviction||1||1||Increases damage dealt to enemies targeting user by 25%||Deal a certain amount of total damage||4,000||"I've becoming stronger."|
|2||2||Increases damage dealt to enemies targeting user by 30%||Deal certain amount of total damage||8,000||"This is only the beginning. Here's where we get serious."|
|3||3||Increases damage dealt to enemies targeting user by 35%||Deal a certain amount of total damage||16,000||"It's not over yet. Don't get careless."|
|4||4||Increases damage dealt to enemies targeting user by 40%||Deal a certain amount of total damage||32,000||"Let's keep this up."|
|5||5||Increases damage dealt to enemies targeting user by 50%||Deal a certain amount of total damage||48,000||"You've helped me come so far... Thank you."|
|Steadfast||1||1||Boosts Break resistance by 30%||Use Theory's favorite pouch items (Board Games Category)||2||"Do you enjoy playing board games? I find them... OK, I guess."|
|2||2||Boosts Break resistance by 40%||Block an attack||5||"I will support you to the best of my ability. Are you concerned?"|
|3||3||Boosts Break resistance by 50%||Block an attack||7||"I won't forgive anyone who tries to hurt you."|
|4||4||Boosts Break resistance by 60%||Block an attack||9||"I have your back. I swear, I will protect you."|
|5||5||Boosts Break resistance by 70%||Block an attack||10||"Don't worry. I won't let you come to any harm."|
|Field Skill||Ice Mastery||1||1||The power of an Ice Blade|
|2||2||Defeat Dusky Riik at Spirit Crucible Elpys||5||"I've become quite proficient with ice now."|
|3||3||Defeat a Kustal Sovereign at the World Tree||5||"Tell me if you need any ice. I'll turn them into sculptures."|
|Focus||1||1||The power to focus on one thing. Also used to control one's power|
|2||3||Use Theory's favorite pouch items (Vegetables category)||4||"Vegetables really aren't bad."|
|3||4||Use Theory's favorite pouch item from the Vegetables category||4||"Steamed Veg Stralu really...warms you up from the inside."|
|Nopon Wisdom||1||1||Knowledge related to Nopon. Decode writing, speak Nopon, etc.|
|2||2||Speak to a Nopon||30||"How is it that Nopon are irritating, yet lovable creatures?"|
|3||3||Use Theory's favorite pouch items (Board Games Category)||2||"Ah...I could get used to this. This is fun..."|
Theory is first met as a quest-exclusive Blade boss during the quest Crystal Clear, where she fights as Plunderous Theory. She is fought at the beginning of the quest on Obra Street in Torigoth, Gormott Province at level 33 alongside Piratical Praxis. Later, she is fought at level 48 as a quest-exclusive enemy during the quest Pest Control 3 as Mediator Theory, spontaneously assisting the group of Cherys Medooz in Lud Cloudway: Fonsett of the Leftherian Archipelago. She does not need to be defeated in order to complete the quest.
|Magnet Chip||Core Chip||12.6%|
|Evasion Focus II||Aux Core||9.0%|
|Metal Nopon Mask||Accessory||6.0%|
|Metal Nopon Mask||Accessory||4.0%|
|Common Core Crystal||Core Crystal||5.0%|