The Hayashi clan and Mayumi.
What the human gains will depend on the animal they bond(most will begin growing fur, not everywhere though, the best comparison would be a super saiyan 4 from dragonball gt), for example if a bear was bonded the clansmen would receive increased height, strength
My Little Pony: Two Worlds United (Preview)
"and when it was like this, with the yellow, they thought i went 'super saiyan', so they started calling me goku. until the highlights went away when i got a cut."