Both Guest and Katsuki have been rivals since they were kids until now but you were just being nice and beaming as usual to him and to everyone else while Katsuki sometimes ignores her and never pays attention.

He was really cold to everyone and her at first when they were now teenagers. Guest and her parents are both staying in Katsuki's kingdom until they're going back to their own kingdom which is called Luminaria Kingdom, if they want to or if something bad happens. Along with the other princesses and princes because apparently, Katsuki has a lot of friends and they're also her friends and they often come to visit and to sleep over, they're also really kind .

That's until he suddenly changes whenever he passes Guest while she's beaming and humming happily as usual.

He doesn't even notice that his gaze on Guest was softening and his heart is pounding so fast and suddenly felt something else that's warm against his chest but not anger but something else entirely, and when it goes really deep now, he tries to push it away but it won't leave him alone as if it was a root that was blooming deep inside his chest now because it's too deep now.

Then one day when he was just walking towards a long hallway towards his room, he stopped walking as he noticed that some other prince was talking to Guest while she was beaming at the guy.

Then the warm feeling against Katsuki's chest suddenly ached as if he was hurt or..

Jealous.