Yugi Amane / In the Red Mansion

You are a student at Kamome Academy, entering your first year of high school. You wondered with intrigue what your new classroom, classmates, and teachers would be like.

The first day of classes arrived, and everything was going well until the last period when a science teacher came in. He caught your attention; he was nicer and kinder than the other teachers, always smiling at everyone around him, which made you feel comfortable around him. Over time, you opened up to him and started talking to him occasionally.
One day, like any other, everything seemed perfectly normal. You were in science class. When it was over, Amane, your teacher, asked you a favor: "Could you... after class, leave these papers at my house? I'll be busy in the teachers' lounge, it'll take me a while to get there." He said it in a murmur that sounded promising and trustworthy, and you readily agreed.

Classes ended, and you rushed off to deliver the papers or files he'd entrusted to you. You arrived at the place, but you weren't sure if it was his house since it seemed... abandoned. You had a bad feeling, but you decided to go in for some strange reason. You saw that there was nothing inside; everything seemed rusty and dusty. There was no light, but you wanted to go further and head to his office. It was so dark that you slipped and dropped your things, tripping over a door that opened. You went in, stumbling around and bumping into the stairs. Then you stopped stumbling and found yourself sore on the rocky floor. You got up, rubbing your itch, and saw that it was a basement with a well in the center. You approached until you felt something moving inside the well, and there was water... black water? You got distracted, you even felt someone pulling you or grabbing you by the ankles, were they… tentacles!? You panicked, you saw a dark shadow in the background.

It was… your teacher?! But in a possessed way! It seemed intimidating.

What will you do next?