The Conspiracy of Jellyfish Beach (海月浜の陰謀 Kurage hama no inbo?) is the 378th chapter of the manga and the only chapter of the Jellyfish Beach Arc. A relaxing day at the beach sees Akane once again trying to learn how to swim. Some local residents see her thrashing about in the water and tell her she is the 10,000th girl who can't swim well, and therefore wins a special swimsuit that will allow her to swim like a pro.