I'm not sure Edith was in the original novel, where he was the male lead and where he got the title 'Tyrant' from in the first place. And he is totally a tyrant. No matter how much she tried to change him in the beginning chapters he remained pretty rude and arrogant.
She was in the original novel which is why the MC knew that she was going to die even though she did nothing wrong. Granted the original sister’s personality might not have been as tough but still
Also he’s like 10. I’ve met plenty of stupid ass 10 year olds. Sure he’s rude and arrogant but aren’t a lot of kids like that to some degree because they still believe the world revolves around them? I wouldn’t call kids tyrants for being stupid.
And imagine a kid suddenly being told he’s the most important person in the kingdom. Of course a kid is going to let it get to their heads. I would have at his age. I totally would have trolled my older brother if I found out I was an empress. Like telling him to kneel. But would I have really meant it? Nah. And that’s what I’m seeing from this kid.
He’s an ass but he loves his sister in a realistically sibling way. He still sees the world naively and can easily be manipulated by those around him.
His personality isn’t great to begin with but I can see how he could have been turned into a tyrant by the princess who wants him out of the castle.
I can’t see Kai turning into a tyrant unless the evil princess manipulated him to be that way and made it seem like he was worse than he actually was.