Phalanx

Using this feat allows a character to pass through an occupied space of a friendly creature of their size or larger without penalty. 
Allows characters to occupy the same space of a character of their size or larger with no penalties as long as both characters have this feat. 
When two characters who possess this feat occupy the same space and are using shields both characters' ACs are increased by 2 points.
Note: Characters can only fight from the same space if neither character is using a weapon with the heavy or two handed properties.