The episode follows Kiruko and Maru, an unlikely duo, who find themselves facing a vicious bear while investigating a location marked on their map as a source of clean water. Using their wits and unique abilities, they manage to fend off the beast, but not without realizing that the map was a trap.

The dynamic between Kiruko and Maru is undeniably compelling as they navigate their strange circumstances and try to make sense of their growing bond. Their comedic banter and playful interactions create a lighter atmosphere amidst the series' darker themes. However, the episode also highlights the uncomfortable aspects of their relationship, such as when Kiruko allows Maru to touch her, leading to an awkward and tense situation.

The characters find themselves in a hotel run by Totori, a young girl with big ambitions. While Maru and Kiruko grapple with their personal dilemmas, Totori throws herself at Maru, leading to a confusing discovery: Maru's power, which was thought to only affect Kiruko, seems to work on Totori as well. This raises questions about the nature of his ability and Totori's identity.

Meanwhile, Tokio experiences a strange dream at school involving Asura, a mysterious figure who appears to have a connection to Kona. The two teenagers find solace in each other, engaging in cryptic conversations and activities that highlight the universal nature of growing up, even in a world where conventional morality is constantly challenged.

Overall, "100% Safe Water" is a gripping episode that balances the humor and lightheartedness of Kiruko and Maru's relationship with the more serious themes of a post-apocalyptic world.