#dark kai

Honestly: Out of all the ninja, I DO believe that Kai is the most likely to turn evil, either by persuasion, mind-control or just willingly. And there are a few reasons why: 

Argument 1: Chen's Staff 

He was quickly corrupted by the power inside of it, and his jealousy for Lloyd only drove him more power-mad. He was blinded by rage, and was, right then and there, COMPLETELY willing to use the staff to destroy Lloyd out of jealousy. Speaking of... 

Argument 2: The Green Ninja 

Even long after season 2, he still held some resentment towards Lloyd for becoming the Green Ninja in season 4, as mentioned earlier. And even though it was kind of dropped after that, I still think there's some jealousy left. Maybe he took responsibility for Lloyd in season 5 to convince himself he was still a good person and still Lloyd's friend. (Also, he understood the struggle of losing his parents.) 

Argument 3: Hands of Time 

When Kai saw the portrait of his parents in the museum, he was questioning whether he'd ever see them again. A few episodes later, Krux manipulated his doubts about his parents when he told Kai that his parents were traitors, and didn't fight in the battle against the Time Twins 40 years earlier. This only fueled his suspicion and made it stronger when he found out his parents made (and are still making) suits for the Twins' army of snakes. One question he asked Nya stuck out to me, and helps support this idea for me: "Were our parents really evil? Are we destined to become evil too?" I think Kai has wondered this himself more than once. And it all hit rock bottom when he saw his dad in the blacksmith shop at the Twins' base. He wasn't just angry, he was ENRAGED. LIVID. He was willing to hurt his father because of how betrayed he felt, even to the point of using his powers. And regarding that... 

Argument 4: His powers 

Whenever he uses his power, it often gets stronger when Kai wants to protect those who are close to him, and that's one of the most relevant emotions that fuel his fire - protectiveness. Another emotion is determination. BUT, it also comes from rage, like when his power returned in the last episode of The Ice Chapter (part 2 of season 11). And I think this is one of the most important factors of him potentially turning evil. His power is fire, one of the most destructive elements. Although this can be left up to speculation, I think that at one point or another, he's thought of this himself. How destructive his power is. Is he afraid to lose control of it? What damage could he cause, intentionally AND unintentionally? Would he be willing to not let his fear limit him, and use his power without hesitation? If so, would he even be afraid to hurt people in the process, both strangers AND his own team - his friends, his brothers, his family? Who knows.