The story is based on a real story of the residents of the island of Miyakejima, which erupted in 2000 and had to be evacuated.
A family, Matsuo, Takako, Matsuo's mother Fusako, and Matsuo and Takako's young son Shin live on the island of Miyakejima, 200 km south of Tokyo. Together, they run a small bed and breakfast for tourists and have two pet golden retrievers, Hana and her son Rock. Shin is in charge of taking care of Rock every day, and despite some typical rambunctiousness from Rock (including peeing on Takako on multiple occasions), they lead a happy life. However, Hana becomes ill, consuming Fusako's attention, and the island starts to be hit by multiple earthquakes, causing visitors to cancel their reservations at the inn.
Soon they find out the source of the earthquakes - the island's volcano is erupting. The family initially don't want to evacuate because they have lived on the island their whole lives. But after a while, with the whole island covered in ash, the residents decide to send the children off to Tokyo for school to keep them safe. Shin doesn't want to leave his parents and Rock, who he has promised be with, but he has no choice.