is one piece episode 991 filler?

Angry that the Big Mom Pirates' ship was knocked down the waterfall twice, Perospero rides to Onigashima on his candy slug. He swears revenge on King and Marco for knocking the ship down.

Chopper's tank fires several rounds at Big Mom but she is unharmed by the fire. She prepares to use her Devil Fruit powers on Usopp and Chopper, but upon hearing Prometheus' call, she walks away.

Although the tank is unharmed, a transformation switch is activated, turning the tank into the lower half of the General Franky. Chopper must unite it with the Kurosai FR-U IV to form the full General Franky.