Four high school girls lie sprawled on a sandy beach. After an accident strikes their class trip, the girls find themselves stranded on a deserted island. While the four introduce themselves, one of them, Onishima Homare, seems unusually calm. Then she says something shocking! "This isn’t the first time I’ve been stranded."

In order to procure water, the girls explore the island. Homare and Asuka find a dry stream bed. In order to get water from the dirt they dig up there they’ll have to…!? Meanwhile, left behind on the beach, Shion and Mutsu, both faint from dehydration, make a certain promise…

Homare and Asuka enter the forest to find food. Asuka is overjoyed to find a plant that looks like taro, but Homare points out it could be dangerous. When Asuka throws a tantrum saying she wants to eat it, Homare gets fed up, suggests they check to see if it’s even edible or not, and suddenly flips Asuka’s skirt up!?

Homare and Asuka go diving for food. When underwater, human vision blurs, however using a certain technique creates improvised underwater glasses which they use to look for turban shells and oysters, but… The severe conditions begin to take their toll on the girls both mentally and physically. Homare remembers something her father taught her — "When things are tough, when you’re sad, have a barbecue."

Asuka and Mutsu go to check the trap they set. Just as they’d hoped, there’s a rabbit caught in the trap, but there’s no time to call in the reliable Homare! If they leave it, it might get away…! What will they choose to do for the sake of survival?!

To prepare for the possibility of their cast-away life lasting longer than they thought, Homare and the others decide to explore the island, and they spot, of all things, a house! With hopes of rescue rising in their hearts, they race forward, but what they discover is the ruins of an abandoned building… Noting the despair of the other girls, Homare finds an item they’ll need to survive the island!

While exploring, the four girls spot a column of smoke rising and speed toward the rocks by the beach! Could there be people…? But what they find is…a hot spring?! They soothe bodies and spirits tired from their explorations together!

Everyone wants sunblock in order to evade the UV rays of summer. That’s where the squid and seaweed Homare brought back come in… When confronted with all the difficulties of a survival situation, from bug bites to reeking of sweat, Homare remembers what her father taught her.

After following the honey bees that have been flying around the camp to their hive, the girls decide to try to get the honey. It isn’t uncommon for people to die from bee stings, so how will they manage to deal with the bees?! Then, Shion boards a raft to try her hand at fishing and gets caught up in…

Shion has been swept away by a rip current and the others are at a loss. That’s when Homare decides to build a new raft and go after her! She breaks her fathers rule of "you own life comes first," risking her life to go save Shion, but in the vast ocean, Homare can’t find her… Having exhausted every option she can think of, suddenly Homare remembers one of her father’s teachings…!

Homare finds the solitary island where Shion washed ashore and the two are reunited. But there’s no time to rejoice. With no food or water, succumbing to dehydration is only a matter of time… All they have is filthy water they find in a cave… In this dire situation, the two of them use a secret technique for rehydration!? Will Homare and Shion make it back to the island?