The Dojo Master is Yareni. She's one of our most venerable matriarchs, and probably the ultimate authority on Crystal and Toxic Temtem. She studied in Cipanku for many years.
During the quest Shipwrecked in Tucma!, the player visits Yareni to clear their name after being accused of committing crimes throughout Quetzal. Yareni challenges the player to a battle, stating that people's true selves are revealed through battle. After the player's victory, she remarks that a scoundrel would never have fought the way the player did, and declares that they are innocent. She informs the city guards of the truth, and the player's name is cleared.
Oh, you're back, Player. The nerve to come see me after all the grief you have been causing in my city. If it weren't for our sacred hospitality traditions...
A great fight... and an honorable one. That is not how you fought last time...
Anyone can dress up in another's clothes, imitate another's accent, throw around another's name... but in Temtem fighting we all reveal our true selves.