Biology teacher Ms. Tsudo becomes possessed by an ancient Lust-demon after analyzing a mummified relic, leading her to drain the life force of men to sustain the beast. The demon eventually targets a virgin student named Reika to serve as a vessel for its offspring. After a desperate struggle to save Reika, the demon is defeated, leaving a lasting impact on the survivors and leading Reika to follow in her teacher's footsteps years later.
Four high school students crash a camping trip for their teachers, Yayoi and Tatsuya, only to be stranded in a dense forest by a sudden storm. As food runs low and tensions rise, Tatsuya reveals a dark secret about his past as a biological weapons researcher. Having discovered the Garanta, a mind-altering parasitic plant, Tatsuya descends into madness and captures Yayoi, intending to use her as a host for the creature's reproduction.
After a storm separates a group of students and their teachers in a dense forest, they fall prey to a horrific biological weapon known as the Garanta. While Mr. Kubo exploits the chaos for his own desires, a corrupted Ms. Mizuno begins hunting her former students. In a bloody massacre that leaves nearly everyone dead, the parasitic entity finds a new host in the sole survivor, Shiori.