A Terrible-Monster Dances on a Sea of Rainbow is the thirty-fourth episode of Ultraman Ace.
While investigating a series of vanished ships, Seiji spots a boy floating in the ocean and rescues him. Seiji takes the boy, Yuji, home, where he meets Yuji's sister and learns that Yuji's mother is dead and his father, who is a captain, is missing. Yuji tells him he is trying to collect one thousand shells so that his father will come home.
- Ultraman Ace Volume 9 features episodes 33-36.