Operation retake Okushiri Island continues! Various teams compete to clear out as many monsters as possible. Overseeing it all is Masatsugi, the strongest adventurer. Haruki's team has been impressing their live-stream viewers until disaster strikes. A massive hole opens beneath their feet, landing them in an underground dungeon and separating Haruki and Karen from Akane. As the two look for an exit, they stumble upon an underground lake and the boss that dwells within it. Can Haruki come up with a strategy to beat a foe that commands the waves?!