Tatsui no Gen (達意の言, Speech of Conveying) is a Power of Unrestraint commonly used between Crimson Denizens and Flame Haze to translate their speech when they speak to each other or to human beings. It is activated when the user wills their speech to be translated.
In Crimson Denizens' case, if the spell was performed poorly, their words would sound like "something which shouldn't be pronounceable". Even when correctly used, the spell cannot conceal an uncomfortable feeling caused by the voice itself, as one cannot feel the flow of air through the throat. But when applied along with their ability to Humanize, Denizens are able to perfectly assimilate into human society. Although not clearly stated in the story, it is speculated that as long as the voice is heard, speechs translated by Tatsui no Gen can be understood via transmission like television or telephone.
Tatsui no Gen can also be applied as a dictionary. When Sydonay was listening to Tiriel talking about her Treasure Tool, Orgel, he used Tatsui no Gen to understand the meaning of the word as "music box".