Nebula, a giant reptilian monster, emerges from a hillside and kills two travellers on a bridge.Years later, in 1909, a boy named Eiji returns to his hometown in Kyushu. Raised by relatives, he knows little about his mother or recently deceased twin brother. He is startled to find a blind cousin, Takiri, also living with his mother. She instructs him not to tell his mother they've met, as she's supposed to be dead. That night, he spots her walking to the lake and follows her. Humming softly, she wakes up Nebula, who now resides in the nearby lake. Terrified, Eiji flees.The next day, Eiji overseas developers trying to convince his mother to sell the last of her land to facilitate the construction of a dam. She refuses, as her family has worshipped there for generations. They note, dismissively, that Eiji is the last male in her family. As she and Eiji eat breakfast, she reluctantly explains that Takiri is her sister's daughter, left with her after the sister committed suicide. Believing that Takiri has gone insane, she has done her best to hide her from the town. He visits Takiri again, who offers to take him to see Nebula at dark. Rumours of the creature have spread in the village, and four of the developers conspire to flush him out.Takiri holds her hands over Eiji's eyes as he reaches out to touch Nebula's face. As she removes her hands, Nebula disappears into the fog. The next day, the developers drag them outside and kick Takiri into the lake. As she falls, she remembers her mother, who blinded her before taking her own life. Nebula comes to her rescue and lets Eiji take her from his jaws. The developers fire on the monster, but to no effect, and he chases them into town. As he lunges at one, he knocks paper lanterns to the ground, starting a fire.Eiji and Takiri find his mother's house destroyed. Dying in the ruins, she apologizes to Takiri for shutting her away and tells her to leave with Eiji. They resolve to try and stop Nebula's rampage. The developers use fireworks to lure the monster to a bridge, where they are waiting with a hand cannon. The blast topples Nebula, but he recovers after Takiri goes to him and dodges the next two shots. Inhaling fog, he knocks three of the men off the bridge with a blast of wind, then crushes their leader.Nebula returns to the lake as Takiri tells Eiji they're now free to go wherever they please.