The last summer. Friends. And Kaiju--.

In the summer of 1989, Boko, Joe, and Junichi, all sixth grade elementary school students, were having their last summer vacation. Each of them is worried about their future. Brody, the son of a US military commander, appears before the three of them and steals away the money they have saved together. Boko and his friends are furious and plan a plan to get their money back. As they are about to carry out the plan, the town is threatened. The kaiju Gyaos suddenly attacks Tokyo. The four are petrified in a town ruined by Gyaos. As Gyaos sets its sights on them, a huge kaiju appears. Its name is Gamera.

This is the beginning of their "Summer of Kaiju." Kaiju appear one after another, and Gamera fights back despite his wounds. The boys witness the legend.

[Source: official website via Crunchyroll News]