FAILURE
Although All God's Village relies on the Crimson Sacrifice to appease the Abyss there is always a chance of the ritual failing. A ritual can end up in failure one of three ways. The first reason being that the twins performing the ritual love each other too much to go through with it. Secondly, if the twin being sacrificed is not dedicated to the cause and does not want to die the ritual will fail. Lastly, it is a popular theory in the Fatal Frame community that for the ritual to work one twin must resent the other in some way. If there is no resentment present the ritual will fail.
It's very obvious why Itsuki and Mutsuki's ritual failed. Itsuki and Mutsuki loved each other very much and found it horrific how the village could actually sacrifice twins to appease the Hellish Abyss. The boys believed that there had to be some other way to appease the Abyss thus leading to Mutsuki not wanting to die.
Itsuki and Mutsuki had no resentment towards each other leading to another factor as to why their ritual might have failed. The one reason Itsuki and Mutsuki went through with the ritual was to spare their close friends Yae and Sae.
Itsuki had a feeling that their ritual would fail. Reading Bound diary 1, Itsuki states that if their ritual fails Yae and Sae will have to be the ones to perform it next. If Itsuki was confident in the ritual I believe he would have never mentioned anything about it failing.
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