You were a normal human teen as of yesterday. And your parents were normal humans too.
You awoke & knocked your tail into your nightstand; which hurt. Wait, tail? You got up with a start & saw it. A long pink mouse-like tail attached to you. The shit?! You were also surprised to see your PJs had a hole for your tail. "The hell?!" You yelled confused. Some reason this seemed to cause your parents to enter the your room. To your further shock you saw your parents had mouse tails too. "What's wrong?" Your mom asked seeming confused. "We had mouse tails!" You pointed out. Your dad replied to that with a smile "Of course we do son." Dumbfounded you asked "Isn't that odd to you?" "Why would it be?" Your mom asked. "We always have." Your dad informed you. Your head was spinning now. [They believe this is normal?] You thought confused. They sent you off to school after this. Even weirder still was no one saw your mouse tail as odd. It was normal to everyone for you to have it. In the cafeteria you were very surprised to see him. It was Brad but way different. He was a snake creature akin to a naga or something. He had no legs only a long tail, a snake head, 2 arms with hands with 2 fingers & a thumb, had no body hair, a scale pattern similar to a python & was totally naked. Everyone apparently thought he was totally normal too. He slithered right up to you & hissed "Hi prey." Gulping in fear you asked "What you say?" He pulled you out of the cafeteria & whispered in your ear "I know you & your parents are becoming mice." You tried to play it off "I don't know what you talking about. I always had this tail." "And I always was this. But we both know better. Reality has changed." He told you. "What?" You asked. He told you circling you "As the days pass you & your parents will wake more & more mouse. Only you & I will be aware of this. Everyone else will just remember you as having this mouse part or that mouse part. Your parents won't be aware. It's worthless to tell anyone about any of this because no one will believe you & your parents are becoming more mouse by the day." "I'll tell people." You informed him. He laughed saying "The next day all you said about it will be forgotten; as if it never happened." Somehow you knew he was right in all he told you. "Why you telling me all this?" You asked puzzled. "To instill fear in my meal." He told you. Telling him off "I won't be a mouse for you to eat." Brad gave a reptilian smile & told you "You will ultimately become nothing but a mouse I bought from a pet store for me to eat; you & your parents. No one remember you but me & your parents. And your parents won't care about your life as long as they live. They will abandon you to save themselves & think nothing of it. Mice don't care about each other. Not that it matters because I'll be eating them too." "I'll run away from home." You told him. He laughed at that. "Pointless. Regardless of what you do you will wake in your bed each day; you & your parents are fully mice. You will then be mice I bought to eat because I'm a snake creature. Your fate is locked. Reality is shifting to make all I tell you true. You will end up nothing but a lowly mouse & I will eat you. You can do nothing about it." Somehow you knew Brad was totally correct. You & your parents were going to end some lowly mice for that damn snake creature is going to eat. No one will remember you & your parents at all but that snake. "See you tomorrow prey. Hope you taste good as a mouse." He said slithering away from you. You were filled with the sheer terror of what was going to happen to you. You knew in your soul that from this day on you are counting down to being devoured by the snake creature Brad. You're not sure if it makes it worse or better that your parents will never see or believe it's coming.
Regardless. It's unavoidable.