Kyatto Keisatsu Beranmee (cancelled Samurai Pizza Cats sequel treatment; early 1990s)
Sometime after the airing of Tatsunoko's 1990-1991 anime Kyatto Ninden Teyandee (aka Samurai Pizza Cats), rough plans were apparently made for a police-themed sequel to be titled Kyatto Keisatsu Beranmee (キャッ党警察べらんめえ Cat Police Beranmee). However, it never got past the very early planning stages, and Tatsunoko and the involved staff went on to other projects.
It seems that the existence of this project wasn't revealed to the public until 2012, in a booklet accompanying the show's Japanese DVD release. Around the same time, character designer Noritaka "Tenko" Suzuki mentioned it on his blog. He stated that the basic concept was a team of Edo-era secret police cats VS. a corrupt force of cop dogs, and that the protagonist cats were almost carbon copies of their original counterparts. Later that year a fanbook was released that contained a single page of assorted concept art by the aforementioned designer, although said page also states that the story treatment written by Satoru Akahori, who was also head writer of the original show, could not be found. At this point, it's unknown whether this story treatment may ever be found and shown to the public, along with any further concept art that may have existed.