If I'm not mistaken, all of the Maricha from the last frame comes from different stories of other artists, like the middle colored Maricha is yuppai (or sokurateisu) while the bald above him is from boshiherondasu or the left front one is takumi, but I could be wrong though. So, excluding that frame, the story did seem pretty straightforward, expedition squad Maricha got annihilated because they're dumbass (no idea whether they're pets or not).