Bathtub ni Notta Kyoudai: Chikyuu Suibotsu Ki
バスタブに乗った兄弟～地球水没記～
On the morning of his seventeenth birthday, Haruo discovers his room is completely flooded. To escape the water, he takes shelter in the bathtub, only to find himself trapped alongside his older brother, someone he strongly dislikes. As the water continues to rise, the two must work together to survive. The situation appears to be part of a larger crisis affecting the planet. Their temporary refuge in the bathtub becomes their makeshift boat, and they set out to see how far it will carry them.