During their vacation, Rin Yamazaki and her friends get lost in a mountainous area. Suddenly, they're forced to stay with a mysterious old man when their car stopped working. During their stay, they encounter some weird things happening to the group. Rin has strange dreams about being under water, Yuka swells up and keeps saying she's cold, and the guys start turning violent. What's more, the man who let them stay is gone and they are unable to contact help. Is this the curse of the mermaid in the legend or is there something more to these events?
Rin is the lead female protagonist. Throughout the game, she has a bunch of weird dreams about being under water. She's also regarded as the dumb one in the group, which is why Seitaro tells her to go to him if she has any questions. Despite her lack of smarts, she does figure some things out on her own such as why Yuuta starts acting weird and what is needed to save the women used by the Tsuchida men.
Seitaro is the lead male character. He is always bickering with Rin, but he withholds some insults because of their predicament. He's regarded as the smart member in the group since he tells Rin to ask him anything. Later in the game, he is possessed by one of the Tsuchida men's ghosts and tries to kill Rin.
Yuka is the secondary female character. She's the first one to get hit by the "curse" and is immobile after the old man leaves. She speaks to Rin through a dream and begs her to take her back. One possible choice for her is to ignite the fire place to warm her up, which will kill her. If the fire place is unlit, she can either be saved in the good ending or she can be left in her swollen state and never return to normal.
Yuuta is the secondary male character. He is the one who unintentionally led himself and his friends to the swamp. After Yuka's transformation, he suddenly becomes fascinated by the paintings of Ophelia's death. When Seitaro asks Rin to give Yuuta a lantern and lighter, Rin overhears him masturbating and saying Yuka's name. Later, Rin confronts Yuuta who is staring over Yuka's bed. He chases after Rin while she destroys the Ophelia paintings. Once all of them are knocked down, he returns to normal and doesn't remember anything that happened.
The old man is a mysterious person who Rin and her friends meet. At first, he helps them out by letting them stay at his mansion while they wait for their car to be fixed. After they spend the first night in the mansion, he tells them that he will be visiting someone in a town over. Depending on what the player does will affect how the old man will turn out. The good end will reveal who he really is and what his intentions were from the beginning.
Bad End 1: Yao BikuniEdit
This happens if Yuka, Yuuta, and Seitaro all die. Rin goes across the swamp and finds the area where the mermaid corpses are. She will be locked in the room for days and eat one of the mermaids' flesh. The old man will find her covered in blood and curled on the floor, horrified by her actions. The old man convinces her that she will be immortal from consuming the mermaid flesh. The game will end with her running through the forest, laughing maniacally.
Bad End 2: Forever DeepEdit
This only has Yuuta and Yuka die first. Seitaro and Rin discover the mermaid room and are horrified by the sight. They will return to the mansion and, thinking there is no hope, drown themselves in the swamp.
Bad End 3: SecretsEdit
If Rin chooses to dodge Seitaro's attack in the old mansion, he will return to normal and, after taking an axe injury to the stomach, drowns himself in the swamp. Rin becomes depressed over his death and weeps by the swamp's banks. Yuuta comes out to confront Rin about what just happened and she confesses that Seitaro is dead. She then hallucinates that he's on the other side of the swamp and jumps in, drowning herself. Yuuta, bewildered by his friend's sudden death, is shot by someone off-screen and falls in the swamp. Yuka, the only survivor, is left in her swollen state and is never cured.
Good End: Underwater DreamsEdit
Everyone in Rin's group survives (Rin doesn't dodge Seittaro's attack and she doesn't light the fireplace). Seitaro and Rin manage to figure out the secret behind the corpses and the legend of the mermaid, connecting it back to the Tsuchida men's obsession of drowned women and the Tsuchida women's desire to protect female outsiders. They manage to blow up the underground facility and bury the corpses. They return to the other side and confront the old man who is revealed as Yukio Tsuchida, a descendant of the Tsuchida family. He reveals that he purposefully turned off the power so that Rin and her friends couldn't contact anyone from the outside and he made them take care of the matter themselves. He makes amends to them by giving them a map out of the area and helps them fix their car. During the car ride back, Yuka returns to normal and Rin reflects on the adventure.