The final game is a showdown between Bernkastel and the husband-wife team of Battler Ushiromiya and Beatrice with Lambdadelta mediating. The final game is designed to be a simple mystery story, one completely devoid of any magical influence.
The final game is bound a set of rules which are set out at the beginning of the game:
The definition of 'culprit' is 'one who murders'.
It is possible for a culprit to lie.
It is possible for the culprit to lie even before committing murder.
Characters who are not culprits only speak the truth.
Characters who are not culprits may not cooperate with a culprit.
A culprit must carry out all murders directly, by their own hands.
A culprit must not die.
A culprit must be among the characters appearing in the story.
Purple statements are as absolute as red truths. However, the culprit alone may lie with purple statements.
The Reader will tell no lies. In other words, outside of spoken statements, there are no lies in the narration
[Lambdadelta] guarantee[s] that it is possible to pinpoint the culprit with this information