The demons in cages acted as bait.
If any suspicious movement was spotted, that person or group was immediately detained for questioning and purge.
That's right, purge.
Even without needing the demons to play out as bait, Reinhardt possessed other means.
And by other means, he meant the Trial of Fire.
At one corner of the fortress grounds, emerald flames burned silently.
The fire of Yggdrasil, pure and sacred.
It had the power to burn all corruption.
Any evil, any knight who carried demonic taint, would be exposed instantly.
Only after passing all three trials were knights allowed to officially join the Dawnbringer.
And on the matter of the third trial, nobody was exempt.
Not even Level 8 Elite Knights.
Not even Heroes.
Every single person had to pass through the Trial of Holy Fire.
Naturally, nobody complained.
As knights who fought with their fair share of demons, they understood the inherent nature of the enemy.
