All Blade Quests
Official art of Theory

Blade Quest

Theory

Quest: “Blade-Sharp Memory” — Royal Guard Barracks, Fonsa Myma (Kingdom of Uraya); the quest then spans Gormott, Spirit Crucible Elpys, Leftheria, Mor Ardain, and Temperantia

Ice Chroma Katana TNK From Chapter 7

How to get Theory: Not a random pull: Theory can only be awakened from Theory's Core Crystal, which is the final reward for completing the Blade Quest "Blade-Sharp Memory" (effectively Praxis's second story quest — Theory kills her own Driver to save Praxis and returns to her crystal). Awaken the crystal with Rex, Nia, Zeke, or Mòrag. Getting here at all requires first finishing "Crystal Clear" (Chapter 5+), which rewards Praxis's Core Crystal.

Before you start

Story progress
Chapter 7 or later
Chapter 7 (started)
How the quest unlocks
Activates automatically when you enter the Royal Guard Barracks in Fonsa Myma — Theory hurls a lance with a note that nearly hits Nia. Requirements: Chapter 7 started, quest "Crystal Clear" completed, Praxis awakened, Praxis's Key Affinity level 4 unlocked (1,500 Trust), and — per Xeno Series Wiki — Nia, Tora, Mòrag, Zeke, and Praxis in the party.
Required quests
  • Crystal Clear (Chapter 5+, Obra Street in Torigoth; itself needs 10 Core Crystals in inventory, the "Core Crystal Hunters" rumor bought from the Informant shop in Mor Ardain, and Mòrag in the party; rewards Praxis's Core Crystal)
Also required
  • Praxis awakened and her Key Affinity Lv 4 = 1,500 Trust
  • Party must include Nia, Tora, Mòrag, Zeke, and Praxis (Xeno Series Wiki)

Walkthrough

  1. With prerequisites met, walk into the Royal Guard Barracks in Fonsa Myma, Uraya — a thrown lance starts the quest.
  2. Obtain the Thunder Crystal from the Old Quarry, Uraya.
  3. Go to Garagorm's Arch in Gormott and investigate the lance thrown there.
  4. Complete all three "Pest Control" quests received at Garagorm's Arch: Pest Control 1 — defeat 3 Magno Blants around Sternum Arch, Uraya.
  5. Pest Control 2 — defeat 3 Bodom Grebels at Underground River Lavi, Spirit Crucible Elpys.
  6. Pest Control 3 — defeat 4 Cherys Medooz at Lud Cloudway, Leftherian Archipelago; Mediator Theory (Lv 48) jumps in to help the monsters mid-fight but defeating her is optional.
  7. Go to Nharil Central Plaza in Mor Ardain and investigate the final lance Theory threw.
  8. Go to Lost Capital Judicium in Temperantia.
  9. Defeat Vengeful Waldemar (Lv 53, Theory's Driver); his Spoot Driver and Grep Driver cronies are optional kills.
  10. Watch the finale: Theory turns on Waldemar and returns to her Core Crystal — you receive Theory's Core Crystal; awaken it to recruit her.

Good to know

  • The Vengeful Waldemar fight has a hidden gimmick: Theory's Aerial Flashdance Blade skill is active on him, so every attack he evades counters for 600+ spike damage — keep accuracy up and healing ready.
  • This is a chain: if you never did "Crystal Clear" (needs 10 core crystals held plus a purchasable Informant rumor in Mor Ardain — very easy to miss in Chapter 5), Blade-Sharp Memory can never appear.
  • Post-recruitment, Theory's own affinity chart re-uses quest-style gates (e.g. defeat Impassable Edgar in Tantal for Frost Banish 5) — she and Praxis are the only non-DLC Blades with more than one Blade Quest between them.