Bonus attacks?

7 star Gear X Anakin. Mace Ayala Lumi Fives.
Anakin attacks...Ayala and Lumi get 'bonus' attack.
Anakin is leader.
Mace attacks. Anakin gets 'bonus' attack.
Half my squad is now gone. And now the CPU takes their 'regular turns'
I'm just curious which character is granting the bonus attacks? I don't see anything in the character descriptions. It's hard to counter.
I know Fives has an assist attack power.

Thanks!