To Dare
The so-called "soul techniques" of Sacrum were Visualizations. In Sacrum, the soul was the core of the will. It dictated everything from comprehension strength to will power and disposition. Due to this sort of design, the "soul techniques" of Sacrum took advantage of this, branching out with this core understanding as its core.
In fact, it was precisely because of this that Mental Realm Masters had once been banned by Leonel's Tatsuya Clan. The ability to pressure another with your will and force them to do your bidding was a strength of the Mental Realm Masters and thus a key cog in "soul techniques" for a very long time.
Still, aside from those that used the soul for such nefarious means, the rest of Sacrum's soul techniques relied on Visualization. In the same way, Visualizations could be considered to be projections of the will. These wills took form and provided powerful effects.