A timeline of events for my dumb theory

Kannon "went to the bathroom" and impersonated Genji's voice, announcing that dinner was ready through the door. When Eva opened the door he shot her with the stake launching device, and transported her body to the bed. Hideyoshi heard none of this, as the shower was too loud. He then loaded another stake, entered the bathroom and killed Hideyoshi.

Later, dinner was actually prepared. Genji and Kanon went to the door to let Eva and Hideyoshi know that dinner was ready.

The difference between the episodes is the accomplices that the main culprit selects. Genji and Kumasawa were both in on the plan with Kanon.

The door was unsealed at this point. "There is no way to set the chain from outside the door" after all. Genji sent Kanon to get a cutter, with Kumasawa supposedly accompanying him. One of them set to work drawing the circle with the notes brought by Kanon, while the other ran for a cutter.

That person arrived, cut the chain, and placed the broken off half in the correct spot on the door frame.

Twilight complete.