Bathtub ni Notta Kyoudai: Chikyuu Suibotsu Ki

Overview

On the eve of his seventeenth birthday, Haruo was hoping to finally lose his virginity. But the morning of his birthday, a big surprise awaits him: he wakes up with his room submerged by water! No time to think, and to avoid drowning, he is obliged to take refuge... in a bathtub! Worse than all, he is stuck in it, next to his big brother whom he hates viscerally. Will the two of them be able to survive the rising sea level, while the whole earth seems to be in danger? And how far will their makeshift boat take them?

Source: AniList