Looks the Reimus didn't know how to clean up after themselves since their parents and Big Sis Marisa did it for them and since they couldn't take it easy with Marisa's dead body they just shit and peed everywhere and can't clean up after themselves so they died.
Apparently Marisa went into shock, got diarrhea and died.
Reimu comforted her sister.
When I woke up, both of them were sleeping.
Well, see you tomorrow.