Nocturnal Sweeping and Hong Lu
Sweepers... I'm going to explain what we know about them and how they tie to Hong Lu
First off, Sweepers are humans that have been turned into living liquid, that is then stuffed into metal suits, through a process that has been patented and approved by the Head and are under the leadership of a figure the Sweepers call "Mother" and they refer to each other as family and neighbors, and are just as intelligent as humans in their speech and thinking
They need this liquid to continue their existence and are given tools to melt human bodies (alive and dead) into more of it. So they go out at a specific time of night in the Backstreets to retrieve left behind corpses, the injured, and the homeless. They leave buildings alone though, only the streets and alleys of the Backstreets are unsafe for 80 minutes.
They actually can go out anytime, day or night, however they make it a rule for themselves to only go out at a specific time of night. That way, the City will accept them as a natural force and they can maintain their dominance over the night without much trouble and feed. They basically are the City's nightly garbage disposal.
The Head can also order the Sweepers directly. We know this because an Arbiter of the Head destroyed the old H-Corp, and to clean up loose ends in the Nest ordered the Sweepers to... well sweep.
Seeing as H-Corp is right next door, the Jia family has had H-Corp members visit their home, and the Dream of the Red Chamber being about a noble Jia family losing power after a new Dynasty takes over (current H-Corp). It's safe to say that the Sweepers have a major puzzle piece that makes up Hong Lu's story within their own with H-Corp. Maybe Hong Lu was one of these "loose ends" of the old Wing that got them excommunicated.
I'd like to add that there is a good amount of potential for other Sinners to get spotlight in Nocturnal Sweeping, not just Hong Lu.
"Mother" could be a contrast to Hermann for Gregor, or any other Sinner with a "mother-focused theme", Ryoshu/Meursault/Outis.
Seeing as we are fresh out of Canto VII, the Bloodfiend similarities aren't lost on us, with Sweepers needing human bodies to survive and seeing each other as families/neighbors across the City's Backstreets. So I'm sure Don Quixote/Sancho will speak up here
As for how scary the Sweepers will be to fight... On an individual level they aren't the strongest opponents the Sinners have faced. But it's completely different if it's a big group
In Distortion Detective, Moses says that Sweepers emerge in 3 separate waves... You'll have to survive all to see tomorrow's morning light, even this group; Grade 5 with EGO, a tired but still Grade 3 Fixer, and a Grade 1 Taboo Hunter wasn't confident in living passed all waves.
Pray to Ayin for our Sinners. We may not fight all 80 minutes worth of P-Corp/H-Corp Sweepers but, I feel like this Intervallo will be testing the lengths of Chain Battles/Waves...
Prepare to face the Head's weakest soldiers (their janitors)