Kisaragi (2007)

totally different story-line.. but one familiar with otaku may appreciate this other movie as well.

The stories are different but reaching to the conclusion through smartly communicating with everyone n discussions is important element in both the movies.

Both are about mystery about death.
Both have a narrative way of telling the details.
Personally(IMO), both have a satisfactory ending.

otakus gathered to figure out or solve a case/situation.