At Rank 1, your maximum FP will increase by 5 per Rank.
At Rank 3, you will have gained a way to constantly absorb Focus from the world around you, gaining +2 Focus Regeneration. (This will cause you to recovery 2 FP every round in combat.)
At Rank 5, this method of constant absorption will blossom into the powerful ability to steal excess focus from magic. When a Spell is cast by anyone other than you in battle, you will recover either 20% of the FP cost or 3 FP, whichever is higher.