Mom's Secret (ママサイテー, Mama Saitē) is the eighth episode in Japan Sinks: 2020.
The boat owner shoots a signal flair, commenting that now they will be found, but then caught blood. Go feels sick and he gives them some seasickness pills. Ayumu wakes up at night from noises and sees the boat owner dead and seagulls eating him. As she chases them, a shark surfaces and takes the old mans body.
Ayumu and Go spend the night thinking about their favorite tv show, what food they want to eat and how they will rebuild their house. They see a bottle with water in the sea and take it, but there was a hole at the bottom and it full of sea water. Go tells her that if he dies, she can eat him and wonders what Ayumu wants he to do if she dies, but she tells him she won't die and will survive. Ayumu uses Go's flashlight to signal an S.O.S.
They are late awaken by fish hitting the bottom of their lifeboat as they eat the seashells attached to it. Ayumu dreams of her father still alive, who jokes that his death was a prank and tells them to catch a bird. A fish accidentally gets on their lifeboat, but they are unable to catch it and it escape to the sea again, but they see a bird on the boat and manage to catch it. As they struggle to hold it, the bird pukes the fish it had ate and they take it releasing the bird. They start to eat the fish, but see the boat fills with water and realize the bird must had punctured the boat, but manage to find the whole and patch it before they sink. Later, Ayumu and Go see a shipwreck filled with seagulls floating past them; on close inspection, one of the seagulls has blood on its beak, indicating that it is eating flesh.
A boat reaches them with Mari and Haruo, but Ayumu thinks its just another dream. As Mari keeps calling her, Ayumu realizes this isn't a dream and the family is reunited. Haruo explains that they got separated from Kite, but he is sure he survived. He comments that they realized the numbers Onodera left them are coordinates and Go due to playing war games guesses its near Hiroshima. They make a compass and figure the direction they must go.
As they travel, they see a motorboat and manage to start it, but its still tied to the dock, which is underwater. Mari's battery then beeps and she tells Go that she has a cardiac assisting device and the battery just died. Ayumu says they can charge the battery, but Mari tells her she is already suffering complications. Being a pro swimmer, Mari decides to dive and free the motorboat. She says her goodbyes and final words with Go and Ayumu and dives. She manages to free the rope, but before reaching the surface, her heart stops. Ayumu and Haruo jump in the water and bring her out. They try bringing her back to life, but are not able to.