Putting it here so you can look it up if you want, but have it be a surprise if you'd prefer.

Birthright: Willos will automatically fire your tear effects on their own, as if you gave the baton command, on regular intervals. Effectively increases your damage output, but watch out with explosive tear effects.

Hive Mind: On top of the substantial stat boosts, Willos transform into Level 2 Willos (the big ones that orbit enemies acting as shields when not charmed).