As always your portrayal of KK is as horrifying as the GOI demands. A few issues though.
Business entities similar to GOI-298 or its parent company (the Kabushiki Kawaii)
I don't really see the purpose of denoting this as a numbered GOI, especially since it's only mentioned once or twice. I would say since you explain its backstory in a footnote anyway, either simply call it by its name or refer to is simply as a subsidiary of KK.
From its lower mandible hangs a mouth-like proboscis which acts as its phallus (designated RPC-XXX-A)
I know it's a bit of a meme to give designations to innocuous things but I don't get not just referring to them as pseudopenis and pseudovagina or any variation of that. Giving only the genitals subdesignations and then never mentioning them again just serves to convolute things.
Behavioral psychologists report that RPC-XXX mimics the process of breathing solely as a reflection of its temperant;
I could be wrong but I don't think temperant is a word. Its good to leave it as "mimics the process of breathing" and then go on to mention the missing organs.
Japanese law enforcement investigating a series of unrelated serial kidnappings3 had found and matched several snuff films — based on context clues such as comparing the wallpaper and furniture depicted with witness testimonial —
Just a bit run-on, perhaps just condense it to context clues, or integrate the wallpaper and furniture comparisons into the statement rather than adding an interjection about it
Contrary to the discovery of over 251 explicit images from within a burlap sack buried alongside an instance, the Department of Humanoid Trafficking could not match these images with evidence acquired
Pretty clunky, maybe try switching it around with "The Department could not match any of the 251 images recovered with any evidence" or a similar structure.
Takahashi repeatedly pummels RPC-XXX's flexile cranium leaving a fractured protrusion
This may sound weird but I feel as though the unique attributes of the anomaly aren't really utilized much in these tapes. It's described as catering to impregnation and inflation fetishists but in the tapes all that really happens is its used to procreate, then it and it's children are beaten and tortured. While horrific it doesn't really utilize the attributes previously given to it all that much.
which range from torn papers from coloring books
"torn coloring book pages" would sound less weird
As usual you bring so much pain to the table, it's very hard to read in a good way. Though, I do agree with Rota that the ending is a bit anticlimactic. It sort of works, as a bleak ending to a bleak story if that's what you were going for. Centrally the narrative has potential and its a good KK concept, but the line of the actual story I think could be restructured a bit to better take advantage of it.