So if D2 does research about the place the department store was built at, would he be able to find anything interesting? That it might have been built on a burial ground or site or a murder or a corpse might have been buried there is just a pet theory but since he's frightened a couple people just by suggesting it...he might as well do some research. Though he knows it might just have been ayakashi, in the end.

Also, what happens if somebody catches some of those koi to see if they really are laughing and if they can talk, beyond that?