My guess is the Shinigami is legit due to the fire festival. That's it. It's the actual spirit coming to claim him, but he can see it because of this festival.
This is why I think Hiyori isn't "Hiyori", it's Toki because 1007 shows that the Scabbards couldn't believe who they saw healing them before Fake Oden shows up. Oda hides that person behind a silhouette, but then shows Komurasaki. So either Toki is disguised as her or both Toki and Hiyori or on Onigashima