"The resentment of all souls lost at sea manifested itself as
this boat-sized starfish. Avoid the foam it spews from its mouth and its long
arms to protect yourself from being dragged to the sea floor."
Asteroidean mainly attacks with large water spheres that it launches at Chibiterasu from its tentacles, which must be dodged. It will also attempt to spin quickly and ram into Chibiterasu for heavy damage, during which it is invulnerable. The key to defeating Asteroidean is severing all of its tentacles; this is accomplished by a combination of attacks with his Divine Instrument or offensive Celestial Brush techniques. When a tentacle begins to glow red, it is a sign that it is about to be severed by Power Slash.
After all five tentacles are severed, the Asteroidean will be very vulnerable to attack. However, it will also gain a more aggressive behavior, and will move around the chamber while spinning more quickly and for a longer duration. Additionally, it will use its most deadly attack: a continuous concentrated stream of water, which tracks Chibiterasu's movements and deals heavy damage upon contact. The attack can be fired at any direction, so the safest method to avoid this is to encircle Asteroidean's body, as hiding in a far corner would not work.
After Asteroidean is defeated, Chibiterasu and Nanami may continue into the Sage Shrine.