Moreover, he wouldn't let anyone harm his wifey, he would do anything to keep Lia safe, even if it meant slaughtering the whole world. The fire in his eyes burned with a fierce resolve, a promise that he would become the strongest, no matter the cost.
Rio's actions were driven by his one million visions shown by Goddess. He knew that Drake was not to be trusted, and his gut feeling was backed up by the countless visions he had seen, Drake was one of the main culprits who caused Lia's death.
His mind was made up, and he knew that he had to take drastic action to prevent any possible harm to his wife.
Even though he could have gone easy on Drake, but it was totally useless. He had tried to befriend Drake in many visions he saw, but it had always ended in betrayal. There was no way that Drake would be a good ally in the future because his hunger for power was bigger than his admiration for the girl he wanted to marry.