Overlord of the Prosperous Sea mostly act individually, but there are no absolutes in everything.
A male and a female Overlord of the Prosperous Sea are often in their mating period, so they would act in pairs and give birth to new Overlords of the Prosperous Sea.
When the new Overlord of the Prosperous Sea is born, they would separate from each other.
The female Overlord of the Prosperous Sea would lay her eggs in the depths of the sea, while the male would guard the sea area above.
Unfortunately, they disturbed these two Overlords of the Prosperous Sea.
If they attack the male Overlord, how could the female Overlord not take action? This female Overlord obviously hasn't completely started laying eggs, and still maintains the strength of her heyday.
Now when she takes action, her strength is even stronger than the male's.
In an instant, she killed a Nirvana Stage team member, making the situation of the whole team worse.