Hattori-san could be an earth spirit that attaches itself to a host through a vaguely defined "purpose" or "act of service".
Manifesting as a police officer like he had been in his life, a vow of service as been established between him and the family when he was praised for something like "picking up lost belongings". The implications of that concept became vague over many iterations, but the strangest thing is that he manifests when such a purpose (however mundane, or twisted, even) can be fulfilled.
His appearance under that table is frightening. Not because he can appear anywhere, whenever any of their stuff drops or gets lost, but on what conceptual loophole he can take advantage of to "fulfill his purpose". At the very least, taking a life is not outside of what he can do.
...still, he looks wacky with that spoon lmao