Later we learn that not only is he related to Rhea as was earlier implied but that he is none other than her own father and her murderer and that he has zero qualms about killing her a second time. Even Azurai seems revolted.
The whole invasion of St. Curtis arc. Not only does St. Curtis, a previously peaceful town, get destroyed while the demons are hunting angels but you can see the destruction it's causing. Oh, yeah, and the whole place is burning to the ground during that portion. The fact that Kieri leaves the group, Kinako is split up from Tirol, and that angels are revealed to have been working with demons during the invasion doesn't help it any less. Oh, and it's shown that it's not just angels that are getting attacked. The fact that the same thing happened at Weyville just a few arcs ago doesn't help, nor does the fact that it takes place during the Flower Festival.
Lazuli's return in St. Curtis. Killed off one of the series' Ensemble Darkhorses? Within sixty seconds of her intro! Nearly kills the protagonists? Three times, in fact! If it hadn't been for Azurai, of all people, she probably would have killed them too. And that's not bringing up what else she could have done before finding Rhea and Buwaro, or what would have happened if Kieri hadn't shown up when she did.
Buwaro could turn into a killing machine if anyone one removed his star pendant, in this state he could kill his friends before they could even react and without the restorative powers of hell would have already done this to Rhea.
Semi-berserk Buwaro brutally mauling Lazuli by sinking his teeth into her shoulder, thrashing her like a toy and throwing her off hard enough for their to be a crunch is pretty disconcerting and even Rhea is frightened by it.
When we see Lazuli after her ordeal with Buwaro, the experience has caused her to go berserk.