I find these stories incredibly intriguing. I never knew The Sarah Saga or the FF VII house stories until you posted this thread. They certainly both serve as a cautionary tale as to who you can trust. It's really too bad that the writer of The Sarah Saga got basically ran off and didn't get to finish telling what happened and how they got rid of her finally.
Interestingly, I had an experience with an individual that was very much like Sarah/Cetra/Jen. For the purposes of this I'll rename this individual "John". When I was a junior in high school, I met "John". He was a sophomore and we both shared a love for all things geek. I had really become friends with him because he was into Star Wars and Final Fantasy III (VI). He was big into doing what he referred to as "live action role playing" and finally convinced me to start playing with him and his friends. At first, I found it to be incredibly fun. We all became fast friends. At one point, I doubt you could have separated us. "John" was the DM/GM at all times. He had a terrific visual imagination. With his descriptions it was like being wrapped up in a good book, he took you to the places he was describing.
Things were good for awhile. We played almost daily for a couple of months. Then Final Fantasy VII came out. "John" and I were very excited about it. He disappeared for awhile to play through the game. When he completed it and re-emerged to join the rest of our friends, something was different about him. Something in his personality had changed. We all saw it. He was very moody. There was something dark in his eyes. One of the NPC characters he used when we roleplayed was a character named Quake. He began referring to himself as Quake. He tried to convince us that his true form was that of a komodo dragon. When some of us laughed him off, he snapped and threatened us.
The group started to drift away from him and each other after that. He tried to bring us all back together and when we would refuse he would become irrationally pissed. One particular time, my brother and I were playing basketball in our driveway. "John" lived right down the street from us and saw us playing outside so he walked over. He began a friendly conversation at first and invited himself to play basketball with us. Soon, he began holding the ball for long periods of time and tried to convince us to roleplay with him. When my brother and I took the ball from him and told him we didn't want to, he became enraged and marched into our garage. He grabbed a broom and swung it as hard as he could at my brother. My brother ducked in time and the broom ended up hitting the basketball goal pole. The pole had a huge dent in it and the broom stick shattered. Suffice to say, my parents overheard the commotion and ended up sending "John" home.
I decided that I just wasn't going to have anything to do with him at all after that. 2 nights later he shows up on our doorstep with a gym bag packed full of stuff. He explained to my parents that his parents had thrown him out of the house and that he had nowhere else to go. My parents called the police and invited "John" in while they got the matter settled. "John" told my parents that his stepdad was abusive and hated him and ended up pulling a gun on him. As it turns out, that's not what happened at all. "John" pulled a gun on his little brother and threatened to kill him because he claimed his stepdad loved the little brother more AND because his parents refused to believe he was a komodo dragon.
The police came and took "John" that night. We never saw him again after that. I often wonder what became of him. I wonder if he got psychiatric help or if he grew out of whatever phase he was in. I wonder if he continued with his psychosis. I've never actually tried to locate the guy because I don't really want to associate with him. I just am curious what happened to him.