Kunihisa's faction was named Shingūtō (新宮党) after the town, Shingu where it was based. He had been called "On the military matters, he is like a kami and a oni" from his father, Tsunehisa. But he often looked down on those who did not do well on the battlefield and was obnoxious from time to time. In 1554, he was killed by Amago Haruhisa supposedly after Mōri Motonari tricked Haruhisa into believing that Kunihisa intended to take over Amago clan but one of the reasons may be that Kunihisa had been too arrogant towards young Haruhisa.
The death of Kunihisa and the purge of his faction significantly damaged Amago clan and turned the balance against Mōri clan in Mori's favor.
Amago Katsuhisa was his grandson.