When Volcan told him that they were about to face a bunch of wizards, the first thing that came to Dante's mind was the usual spells, such as fireball or lightning bolt. He never expected his opponent to come at him with something as insidious as a truth compulsion spell right from the get-go.
It didn't feel like something one could defend against, at least not without using one of Volcan's anti-magic suits. Of course, Dante couldn't just put on an armor and expect the interrogation to continue, and even if he had a different way to protect himself against the mental attack, he was sure its caster would quickly notice that his powers weren't having an effect.
Cornered, Dante almost chose to drop everything and try to escape, but then his strained mind led him to an unlikely answer: he just had to say the truth. At first, he suspected that it was just another effect of the spell, but after testing it, he realized that it didn't matter what truth he told so long as it wasn't a lie.
