Khaenri'ah's obsession with the truth is so fascinating, and I believe that obsession comes from Irmin's rule.
In norse mythology (again) Odin was had a great thirst for knowledge and an obsession with seeking the truth, which led him to self mutilation, suicide and self inflicted torture; and eventually he did become all knowing.
With what currently know of Irmin, little as it may be, i think its safe to assume he has a similar story. Aside from the fact that he's one eyed as well, the literal world tree of knowledge aka irminsul is named after him, we know that he had introduced forbidden knowledge into khaenri'ah (and all of teyvat if the irmin=nibelung theory is correct), was actively encouraging shady research and he also built teuvat's biggest university right up there with the akademiya.
It was under Irmin's rule that the most widely practiced sword art came be known as "truthseeker", and it was under his rule that astrologers named their strange phenomenons "signs of truth".
And look at some of the abyss monsters voice lines:
[Let the blind see!]
[Be still and know!]
[Hear the truth!]
[The truth shall set you free!]
[The power of revelation!]
[In the name of the truth!]
[The truth... shall endure...]
[Revelation from on high!]
[Ah... how brightly burns the truth!]
It makes sense with their idealogies as well. The rest of the world is shrouded in falsehoods; a false sky, false gods, false laws, a false rule. So let us, who have detached ourselves from them and established a new rule, be the ones to always seek the truth. Let us be the ones to unveil and decipher the nature of this world, for those who dwell on the surface have their eyes and ears covered by the hands of their gods and will never attempt such a thing.
[False laws begone!]
I wonder if this gave them a sense of superiority before fucking them over.
