>>55460535I feel like it got threatened because it was thrown into battle right after waking up and defeated and pushed further even after that. If Kieran didn't tera the turtle, he'd probably still be able to keep it, the extra energy from the crystals helped Terapagos destroy the ball. I think it attacked Kieran intentionally as the one who kept abusing it but didn't plan to stop if the hit landed.
Or perhaps Terapagos wanted to kill Kieran for breaking the rules that only the protag can catch legendaries. And Kieran realizes that and never, ever competes with the protag in catching legendaries again, refusing even if you offer him to catch one. He's too scared to oppose you now that he realized.
