Gray Parasite

Humanity is being attacked by parasites—mysterious creatures that invade the ear, destroy the brain, and take over the host's body. They can transform the structure of the head and migrate from one body to another, feeding on humans. The parasites produce from one to five tentacles from the head, each with sharp, knife-like tips.
Jeon Soo-in is a young woman who works at a supermarket. One day, she finds herself bleeding in a field when a parasite lands next to her. It attempts to enslave Soo-in but fails to reach her brain. As a result, the creature takes up residence in her body, causing a deadly tentacle to grow from her head. The parasite turns out to be intelligent and is later named Heidi.
Seol Kang-woo is a young man and a member of a gang. He begins searching for his younger sister, trying to determine if parasites are involved in her disappearance. He finds himself in comical and dramatic situations, helping Jung Soo-in as best he can and always by her side. Choi Joon-kyung is a young woman and the leader of the "Gray" team. The team was created specifically to identify and destroy alien parasites. Joon-kyung is a colorful character: tough, a little crazy, and determined. She wears leather gloves, is always armed, and ready to shoot. She is trying to catch Jung Soo-in. Kim Chul-min is a senior detective at the police station. He is unwittingly drawn into a confrontation with the aliens. He tries to figure out what is happening and help Jung Soo-in.
Heidi is a parasite that has infested the body of Jeon Soo-in. Unlike most of its kind, it has not destroyed the host's brain, but coexists with it.
Many parasites hunt for Jeon Soo In to kill her, as she is an existential threat. Heidi herself can only possess Jeon Soo In's body for 15-20 minutes. Heidi speaks little and acts greatly, being very intelligent and strong.
Now, Officer Kim Chul Min has called Jung Soo In to a meeting. Jung Soo In came with Seol Kang Woo because she trusts him. They don't yet know that Choi Joon Kyung is already on his way with a squad to capture Jung Soo In. When they saw her car, Jung Soo In and Seol Kang Woo fled to the old building of horrors to make it harder to find her.