You add your Intelligence modifier to your AC as long as you are unarmored and using your chosen weapon.

Guides generally recommend two primary paths depending on your priority:

Always keep this toggled on once you have Crane Style. The AC bonus far outweighs the small hit penalty. To help you refine this build further, let me know:

The Sword Saint is a 6-level caster. You do not cast Fireball . You cast delivered via your sword.

You must choose at level 1. You will use it forever.