...other than mangle his hand so badly that he could no longer hold a pen properly, much less a sword, thereby making it impossible for him to be a knight of the dukedom/kingdom as he had aspired to be?
...hopefully next chapter will tell us. :3
*sorry, Read comment backwards. I thought it was what did the prince do for Uri to hate him.
As for what Uri did, they sure make the prince of "that time" look pretty crazy so maybe nothing at all. Maybe crazy prince was doing crazy things and Uri tried to stop him, so prince crushed his hand? Or maybe Uri really was being cocky or something and earned the prince's wrath. ---Hard to picture that being the case while the Prince is standing on a pile of bodies and holding a dude by the neck though.
That said, maybe Uri did something stupid like joining a revolutionary faction while training as a knight. He is a really simple, gullible, and easily influenced guy, after all. Maybe he joined a group of people to "take down" the second prince as a way to "help" the first prince or save the kingdom from the "OP 2nd Prince" or whatever. -- Then, in the midst of the attack on the second prince the group got their asses handed to them, while Uri (being important to Lamia) got just his ass spanked and his hand mangled as a way to show he had lost the right to be a knight before the Prince sent him (traumatized, but alive) home to his Dukedom.
yup, that's my theory.
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Damn what Uri do to make the Prince hate him so much????