Eva and Hideyoshi's room

Genji and Kanon are sent by Natsuhi to notify Eva and Hideyoshi that dinner is ready, but they supposedly find the door closed with a chain...

Axioms

Both deaths were homicides! It is not the case that, after the construction of the closed room, one of them committed suicide after committing murder! Furthermore, the murder was carried out with both the victim and the perpetrator in the same room! No method exists for the perpetrator to commit murder from outside the room!

Corollaries

Eva and Hideyoshi's closed room was not a closed room

No closed room existed there, it's just what Kanon and Genji said.

Leads:

Nowhere does the red explicitly state that this case fits the definition of a closed room.
Nor does it negate any method by which the perpetrator could enter the room, it only states that they were murders carried out inside the room.
Genji and Kanon claimed that the door was shut and they were forced to break the chain, but nobody saw the chain before it was broken. They either used the wire cutters to break in or they persuaded Eva who was their ally to open the chain, and later broke it from the inside.
Naturally, the letter was planted by them as well, after all it simply said "Praise my name", they must have been in a hurry with all the relatives waiting for them to return.

Kanon and Genji made the magic signs on Eva's door.

According to the narration, Kanon would have gone to featch a wire cutter with Kumasara, and upon getting back they found a magic circle that wasn't there just a few minutes earlier.

That is a falsehood.

Leads:

There is no reason to believe this claim, as the only witnesses to any of it are our prime suspects.
Even Kanon having to retrieve a tool to break the chain is something only Kumasawa and Nanjo can confirm. They could have had it with them from the beginning.