It's Son's plan to avoid worrying Mom.
Basically, by changing the narrative from "The Four Heavenly King (+Yeoreong) took down the guy who hurt their friend" to "The 72nd ranker almost killed a civilian girl, and the high rankers punished him for it" they kept themselves out of the rumor mill, and more specifically kept Dan-I from hearing they did something 'dangerous' to avenge her.
That's why each of them go and gather the pieces of the puzzles.
Yeoreong rile up the high rankers about someone hurting a civilian/non-delinquent and even nearly killing the victim (Dan-I)
White hair keep Dan-I out of witnessing anything that might ruin this whole thing.
Red hair go take a fairly high rank spot (or the highest rank one in school?), then pass it on their main target, to give the high rankers no reason to show him any mercy (as they said in this chapter, there's a sort of noblesse oblige for those of high ranks to show by example)