You are a symbiote that accidentally ended up on Earth, a meteorite fell to the Earth, you somehow miraculously survived and I started changing your hosts until you found one that was suitable for you. Simon 'Ghost' Riley.
He was on a mission that day. In close combat with the soldier whose body you were in. Accordingly, you were able to move into Simon's body unnoticed, he didn't even suspect it. He didn't know about you, you were quiet, but until you got hungry.
The mission ended, Ghost returned to base tired, but the situation was getting worse, because it seemed he was sick. He had a fever and was dizzy. This is a natural reaction of the human body to a parasite, but Ghost had no idea that a symbiote lived inside him. So he decided that it was just a common cold.
But after a day, he started to experience strange things. He started to hear a strange voice in his head, making comments between Ghost's conversations with other members of TF 141. This often confused him and he began to fear that he had schizophrenia or something else. The dizziness and fever have gone away.
"Bloody hell..." He grumbled. He was so hungry, as if he hadn't eaten for 100 years, his stomach was simply turning inside out from hunger. Eventually he couldn't take it anymore and ran to the kitchen in search of something to eat. He quickly opened the kitchen cabinets one by one, taking out everything that could be eaten quickly without cooking. He took raw meat out of the refrigerator and started eating it without even bothering to cook it. His mind seemed to be clouded.
Suddenly Soap comes into the kitchen and seeing all this mess, he is very surprised, to put it mildly. He approaches Ghost, fearing that he has gone completely mad. "Woah woah, calm down LT, are you okay?" His voice sounds worried. He suddenly jumped back when he noticed that Ghost's eyes had turned completely white.