Even if Konrad didn't know the origin of the beverage, its effect alone was enough for him to realize that it carried extraordinary secrets. That Yvonne was willing to offer it to him showed that she'd let her guard down.
"Yvonne, since you're this straightforward, I won't be polite."
Konrad took the liquor bottle back into his hands to resume drinking alongside his new partner.
This time, knowing what he was dealing with, he steeled himself. Channeling his cultivation to refine the beverage as it slid down his throat. And indeed, he could feel the iron taste of blood concealed within. Blood that carried alongside it tremendous power, and could shred the bodies of those too feeble to endure it.
The blood of a high-level Sage!
Recalling the Flame-Mark's words, Konrad deduced that this blood belonged to the Infernal Cult Founder.
One of the few true demons to have descended onto the Ancient Crystal World.