Four small dragon-like monsters arrive on Earth with a grand mission: to conquer the world. In practice, however, their conquest involves studying human society by freeloading in the apartment of Nushi, a twenty-eight-year-old office worker living in Tachikawa. The monsters, named Mera, Gusuka, Aniki, and Sugar, turn her home into their secret base while perpetually putting off their actual plans for world domination. Rather than focusing on large-scale destruction, the narrative follows the daily chaos and heartwarming moments of this unlikely cohabitation. Slice-of-life episodes explore mundane struggles like dieting, mastering playground equipment, and dealing with rainy days, as Nushi tries to manage a household where her roommates are small, opinionated, and terribly unconcerned with human convenience. The world expands when a neighbor also living with two monster brothers, Gao Gao and Garu Garu, moves in next door. This introduces a secondary human Nushi, who also works an ordinary job and struggles with things like home repairs and workplace stress, while his own monsters look up to a mysterious master known as the Neko Shisho. As the two households interact, the monsters engage in shared adventures such as summer festivals, moon viewing, and creating Halloween costumes, gradually uncovering that these creatures possess secret abilities far beyond their cute appearances.