Kaito's betrayal of Darian wasn't something he did without thinking about it, but something he had in mind ever since Darian managed to save Kalen, because when Kaito saw the Obelisk Golem's core and eyes glowing and realized that it was preparing for an explosion, Darian was already running towards Kalen to try to help him before Kaito even shouted, as if Darian also already knew what was going to happen.
What's more, Darian seemed too calm from the start for someone who was facing a boss for the first time. Unlike Rylan and Zara, who wanted to appear controlled, Darian didn't really seem worried about anything.
And this calmness, combined with his above-normal strength, techniques, perception and everything else, didn't seem natural to Kaito, considering he was still on the second floor.
