Tarasc tends to mega evolve and scare any Gallade that tries to impress Chanela with their blades off with his own. Chanela is of course not worried, she knows that he is actually a sweetheart. (She just doesn't realise he is only to her.)
Tarasc name was inspired by the French legend of the sea serpent/dragon Tarasque, who was tamed by the songs of a French holy woman. From there, the idea came that Tarasc heard heard Chanela sing when she passed the Wild Zone with her trainer and it calmed the Alpha rage in him. When Chanela was in danger, he swooped in to save her and joined the team. He became infatuated with her, something Chanela hasn't picked up on yet, even when they always hang out together. So yeah, he doesn't take kindly to any other Pokemon who tries to court her.
Also like to think that even tamed Alpha Pokemon get the red glowing eyes when angry!