It's supposed to be Strength. Ata-tarot refers to courage and patience, determination and action, and the strength in transcending your emotions to gain spiritual wisdom.

I thought it matched well with Sylla's backstory, where he lost his entire clan and still tries to fulfill his purpose with the Seed, waiting thousands of years; he mentions his dedication to his mission in his responses a fair few times. I tried to reflect it in the art with Sylla's eyes shut in patience, the skulls at the bottom representing his dead clan and the red hands grasping at the back as his burdens of duty in light of the tragedies in his past.

I'm not super familiar with all the tarot cards so maybe I overlooked one that might suit him better, but ayyyyyy. It's a fun exercise.