The quest is unlocked after completing the Testing... Testing... One, Two... quest.
"The fight to stop Calamity Ganon may be over, but battles against monsters who threaten the peace have continued unabated. Share the memories of these difficult skirmishes with Terrako."
"You told Terrako stories of the battles it had missed during its long slumber. The Guardian then whirred into action to reveal a new move, as if to show that it had grown stronger too."
- Terrako: Bonus Combo