Cooperative Swarmer (Combat)Source Blood of the Beast pg. 22
You’re a team player and help out those normally too large or clumsy to fight in close quarters with you.
Prerequisites: Swarming racial trait.
Benefit: You can share a square with an ally your size or larger, even if your ally does not have the swarming racial trait. Neither you nor the creature you share a space with count as f lanking your targets, but you gain a +2 shield bonus to AC while sharing a square with a larger ally. If you perform an aid another action to aid your ally’s attack roll or AC, increase the bonus you provide by 1.