Tsuchinoko to Shiokaze

"Can you marry my older sister, please?"

Murata was just transferred to become the manager of a supermarket branch in Kureshima, an island in the Chugoku and Shikoku region. That's when Aika, a high-school student who works there part-time, suddenly gave him a strange request. He was having trouble with the staff schedule so, when Aika threatened to quit her job unless he meets up with her sister, he had no choice but to agree. However, when he actually went to visit their home, he found it to be a "Tsuchinoko" museum!?

Just what kind of woman will the older sister who runs a museum turn out to be and why does Aika want Murata to marry her sister? Also, what direction will Murata's sham marriage hunting take...!?