Guts is trapped inside the Sea God. He tries to stab at the walls and is engulfed in water/blood. Goes near unconscious, contemplates death. At that moment, the Child appears above him, whose hair is really starting to look like Griffith's now. He guides him to safety by pointing the right direction. From there, the merrows drag Guts out and bring him to safety. Meanwhile, the Sea Horse crew, led by Roderick, enter the mouth of the Sea God's corpse in order to try to rescue Guts. But then the Sea God begins to sink (?). Thankfully, Guts and the merrows meet them just then. The episode ends with a focus on the Child, who was apparently sitting with Casca the entire time (must have been astral projection?).
Isma's mother gives some kind of explanation about the state of the ocean right now, but I can't read it yet.