I belive the chamber Dita and Kuu don't want to go in to be the chamber where the Santification happens, in order to acquire eligible subjects for the role of Saint-Hierach a process known as Santification was performed, this process not only sometimes killed the subjects, but left them with memory loss (erasure/past self being erased by Idea)and some mutations.
The body at the Mechagod ruins seems to belong to Kuuem N.5, according to the Ultimate Stone and the Santification Records.
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The stone mentions a ruler that was once crystallized and to this day remains at the bottom of the world, Kuuem N.5 Trait from Santification was crystallization.
If memory serves Idea left ASYLUM a long time ago, because both Idea and Albus disagreed with Ino when he decided to try and save the calamity from sin, i lost my save but there is a note in the little place Ino's Phantom sits from star dragon Albus telling Ino about it.
That's what i've understood so far, might be wrong here and there.