it was the work at the end of volume 3 (ch21) that they sold at comic A. but its much more expanded in the anime.
in the manga it was a simple UFO vs UFO battle anime with basically no plot (manga eizouken slowly improves and only started to do plots starting with tanuki el dorado) but in the anime they progress much faster, and themes start emerging immediately beginning with their second work about "who is right and wrong" when they show that the school people were eating a ton of crab and hints that the crab monster is only attacking due to his brethren being treated as food, and in the third work, they took inspirations from the town along with the duality of the female teacher being against eizouken but also being an avid gardener who takes care of the school in her spare time (this is completely anime original, along with that ramen otaku guy in charge of shibatama town restoration) and expanded the story into one about coexistence. the whole music being wrong and needing to change the ending etc is also anime original.