Waita (written Y太) is a hardcore guro manga artist. I couldn't find as much on Oyster, but he/she is some sort of H-manga artist apparently.
Mozuya is Mozuya-san Gyakujou Suru (Mozuya Runs Amok), a manga series by Rokurou Shinofusa that's sort of a comedic light-hearted slice of life about a girl named Mozuya who is diagnosed as "Tsundere" (they treat it like an actual medical condition) and her life in school.
Just from skimming the first chapter, there's a character (somewhat overweight with a shaved head) named Bantarou who has a crush on her.
Waita's has a manga book called "Death Face" in which one of the chapters is titled "Cockroach" (Gomimushi originally, but the translated version I found was titled "Cockroach").
In it, a fat bald man who resembles Bantarou, who kidnaps a young girl who resembles Ena, and brutally abuses her.
At the end he turns her inside out.
And that's not a metaphor or sexual innuendo, he literally turns her inside out.