The GaoGaiGar: King of the Braves television anime, part of Sunrise’s Brave Saga franchise, debuted in 1997 and spawned the Brave King GaoGaiGar Final OVA sequel, which in turn inspired the Brave King GaoGaiGar Final Grand Glorious Gathering television anime that retells the OVA’s story with an alternate ending.
It takes place in 2016, eight years after the end of Brave King GaoGaiGar Final.
Sunrise released the first part of the story in June 2017 in a volume labelled as the third book in Yuichiro Takeda’s The King of Braves: GaoGaiGar novel series.
The original story is a crossover between Sunrise’s Gaogaigar and Betterman anime franchises.