basically seung-hyun gave yuta a terminal injury to his head (you’ll see next chapter how he gets this injury.) and right after he receives said injury sh makes a promise to yt he’ll come back to help/save him after he defeats the people coming after them.. spoiler alert he never comes back and yt has always held a grudge since this incident and he’s willing to do anything to get back at him for it (hence forth why all this beef between them is going on)

ohhhhh I finally get the plot it just clicked