Kaseifu no Bukimi

Kotobuki-san, a temporary housekeeper, arrives at the fourth-grader Takuto's house. She is supposed to be here for only five days to take care of Takuto and his sister, who is in the second grade, while their parents are away on a trip. At first the atmosphere is friendly, but gradually strange things begin to happen: Kotobuki-san sets mysterious rules, a neighbor's dog goes missing, and the younger sister falls down the stairs. Takuto becomes suspicious and begins to investigate Kotobuki's true identity. (Source: Sukima, translated)