Midara continuing his quest to beat up the entire Nowa family. I loved the callbacks to Midara vs Mitora in this fight.
@Solano
Kyara had a very aggressive personality. Remember how in the earlier chapters he would threaten to hurt Kaji because he couldn't stand how incompetent he was? (and also he was mad at himself for hating Kaji). Also he was a huge tsundere, and so is Yakou A, haha. Speaking of that, Yakou B is also very aggressive and he seems to have a complex about his brother. Kyara and Yakou are are also obsessed with violence and fighting (Yakou A also has a thing for violence seeing how he loves his job as a "debt collector" and how crazy he got while destroying the cabin Ideal was hiding in. Though his is more subdued I guess).
If by "weird persona antic" you mean like a "character quirk" they all have one. Kyara and Yakou B's I would say are related to how aggressive they are, so maybe an exact "quirk" is harder to pin down. Yakou A's quirk is probably his insistence to make coffee even though he is terrible at it. Mitaka's "quirky aspect" is her catchphrase, "BOY" (it's in English in the Japanese version so it's probably harder to notice in the translation).
So anyway, I definitely would not say Kyara, or the two Yakou brothers have a "normal and collected" personality. The only one that might fit for is Mitaka. Which makes sense because she basically lost everything so she more or less just goes with the wind and doesn't have any loyalties (off topic but now that I think about it, it's similar to Suteguma....) Though I guess she has times when she gets mad or aggressive but its a lot more subdued compared to the other three.
I never really thought about if the character "quirks" had any like thematic purpose. I just assumed they were to create interesting/memorable/characters that stand out. As anime/manga characters are usually very weird/quirky. But imo, the Usogui characters manage to stand out and be "quirky" without falling into any of the usual anime/manga character tropes. So I like them for that. Kinda went off topic there...