Simple answer, think of my character like glorified attack dog.
Complicated answer, I specialize in symbiotic type charaters, or characters who require the assistance of another to truly and fully function.
Examples: A zanpakuto from Bleach. A tailed beast from Naruto. A death scythe from Soul Eater. A celestial spirit from Fairy Tail. A pokemon from Pokemon.
My character cant move, act, or develop without being linked to another. In this case, someone with little or no powers would be best suited, as to keep things fair and even. Someone who already has powerful abilities doesn't need a guard dog.