Blade-Sharp Memory

Blade-Sharp Memory is a Blade Quest in Xenoblade Chronicles 2. It can be received by going to the Royal Guard Barracks in Fonsa Myma, Kingdom of Uraya, after beginning, unlocking Praxis's fourth Key Affinity reward, and provided Nia, Tora, Mòrag, Zeke and Praxis are in the party. Completing it will unlock the fourth level of Praxis's Fierce Deluge. Additionally, completing the quest will reward the party with Theory's Core Crystal.

Quest objectives

 * Obtain the Thunder Crystal from the Old Quarry, Uraya.
 * Go to Garagorm's Arch, in Gormott.
 * Investigate the lance that was thrown by someone at Garagorm's Arch, Gormott.
 * Complete all three objectives:
 * Complete the mission "Pest Control 1".
 * Complete the mission "Pest Control 2".
 * Complete the mission "Pest Control 3".
 * Go to Nharil Central Plaza, in Mor Ardain.
 * Investigate the lance that Theory threw at Nharil Central Plaza, Mor Ardain.
 * Go to Lost Capital Judicium, Temperantia.
 * At Lost Capital Judicium in Temperantia, defeat Vengeful Waldemar and cronies (3).
 * Vengeful Waldemar is accompanied by Spoot Driver and Grep Driver.

Results
"To save her old friend Praxis, Theory turns on her Driver, thereby returning herself to her crystal."