Blue onyx is a stone of  strength, endurance and determination. It encourages self and mental control during stressful situations. It is excellent for centering a person's energies and promoting alignment. 
Both stones are stones that negate negative energy and align your energy, as well as chakras.
Kyanite is a big dog when it comes to protecting and aligning your energy.
It aligns all 7 chakras and cleanses you of any negative energy. 
It is a cleanser, aligner, and protector.