The reason it's called 'that thing' is that Luo Su himself isn't sure of its state or means of preservation.
Benefiting from Yekaterina's excellent maintenance and sealing, Luo Su only knows about its excessively dangerous nature, with no further information.
Moreover, that thing is completely like a Natural Enemy to him, he has no interest in understanding or approaching it.
Even with the most shameless Legion and most versatile Ability of the Heavenly Kingdom Genealogy, Dusk Genealogy still has weaknesses—namely the Sublimaturs themselves.
The miracles originating from the Nordic Gods are too violent and overwhelming, causing great impact on the Sublimatur themselves, leading to shifts in their character and consciousness.
To put it simply, the higher you go, the more you become like the Nordic Gods…
