First starts with a Marisa trying to teach a Komarisa, who's SO STUPID that anything beyond one is 'lots'. One day, while Marisa went out, Komarisa got to taste some good food thanks to her mother, which contrasted with what her father (who isn't paste-related) had always fed her. Because of that, she becomes resentful, and runs away. She eventually shows up as part of a scum group, who takes over the place where another family lives.
There are two factions in the city, a Myon guard group, and the Scum Family, which is like yakuza. Led by Scum Marisa, they conduct raids on human shops, using children born from rapers to distract the humans while they steal food. The picture shows Scum Marisa making a trade with a badged Alice, three unused Koreimu and some food for chocolates and biscuits. Alice has already purchased over thirty koyukkuri... because she's a lolicon raper.
Eventually Komarisa and Scum Marisa hooked up (huh, rare), but given that their usual nest is too small, Komarisa comes up with the idea of borrowing her father's place. However, Marisa realizes who Scum Marisa is and attacks. This triggers Komarisa's memory about her father and she kills Marisa. But a bunch of Myons suddenly pop up to surround the two of them, though Scum Marisa escapes. (I don't get what they did to Komarisa... something about living in isolation)
Then the story switches (I get lost around here). There's some mention of a Godfather, or Godmarisa, a third bunch that want to take down the Scum Family, with a Patchouli, Yukarin, Chen, Myon, Remirya and Flandre. Patchouli leads the attack, taking out a scum Chen by spitting a stone despite coughing a lot. Myon taunts the scum, and pulls out a cake knife from inside her mouth. (Another picture of this anko)
Together they slaughter the rest of Scum Marisa's party, then leave Scum Marisa to their little one... a Rumia. That day, the Scum Family is largely wiped out...
Komarisa and her children eventually die in a heavy rain. (It goes on & on, but she eventually realizes what her father was trying to teach her... too late though)
My impressions when I read this before that it was a single yukkuri gang, with the "Godfather" Marisa as the actual leader and enforcers (led by the Gesu Patchouli and the Gesu Myon pair) wiping out the members who have stepped out of line. (Was also quite confused with the roles of the "God" Marisa and the "Scum" Marisa until your summary cleared it up--seems more like the Scum Marisa was a former underling that struck out on her own). The Myons "Guard" were actually the yukkuri equivalent of the police force in the city, and were working with the humans.