Grius appears early in Metaphor ReFantazio, and you can teach your co-conspirator how to use the power of Archetypes to further your mission. At first, he can pick from three options, each with advantages and downsides.
After the protagonist and Strohl awaken to their new power, you can choose one of three different Archetypes for Grius: the Warrior, Seeker, and Mage. I chose based on the theme, but each choice in Metaphor ReFantazio has merit.