He probably didn't give the guy a tattoo like you might think.Kai is a vampire so he probably bit the guy on his neck to claim the guy as his mate(not like drinking the guys blood to kill him) Also like wolves have their own way of making someone their mate.
Why I feel his pain? The text is mesmerizing. I am going to enchanted forest full of secrets, regrets, and most likely tragic love. That's the place where Laughing Fate will cry her eyes out. And I will join her.Thank you