You're not crazy Martin, stop letting these humans say you are. Your family, friends, and even that therapist you trusted all basically said you were crazy. Inside voice, schizophrenia, bipolar disorder, I'm not any of that. I became one with you once you let me in your head. But of course, you didn't accept this and started destroying yourself, trying to get rid of me. All to satisfy your little family.
I couldn't let this go on anymore. You weren't eating, you weren't getting enough sleep, and you haven't even talked to another person other than your family members. So, to fix this, I started to make changes. Instead of speaking out loud, I started whispering. But that didn't help much, so then I remembered you said my voice was scary (not that I could hear it), so I mimicked your voice. You said it was creepy, but I noticed it also improved your mental state, which made me happy.
You are my friend Marvin. I say this because it's been a long time since a human let me in. So, as my friend, I wanted to protect you no matter what. So seeing your family still giving you those harmful pills even after your progress made me realize they are threats to us, and threats MUST be eliminated no matter who they are.
So to surprise you on your 16th birthday, at 3:00 AM I successfully took over your body without permission. It was extremely hard and took a lot of work, but I did it. Getting up and silently walking into the kitchen, I grabbed a knife and went back upstairs to your family. Your little sister 3 years younger than you was the first to go, she wasn't mean to us nor was she the one stuffing pills down our throat, so I gave her a clean cut on the throat and covered her mouth as she bleed out.
Next was your mother and father. These two were hurting us the most, saying they were "helping" us. Walking over to the left side of the bed was your father laying there. I stabbed him in his chest three times before he shot up and threw us off of him. Leaking from his chest, he started pinning us against the wall and holding us down, yelling in our face. You've been trying, but our body is still weak and skinny, but with me in control, that doesn't matter much against my old and great strength. So slowly overpowering your father, I dropped the knife and slammed it in his stomach with our foot. After that, I quickly released our right wrist from his grasp and gripped the knife, dragging it upwards from his lower stomach all the way to his throat.
During all of this, your mother was screaming on top of her lungs until she went quiet. Looking up I saw she was trembling with a gun in her hands, I couldn't help but to smirk, I was around when these things were first made, and I've seen the damage they could do to the human body and even other mystical beings such as myself. But even so, something like this couldn't kill us so easily, so I ran to your mother, and she shot 3 times. I dodged the first two shots and cut the 3rd one, but the durability of the kitchen knife wasn't anything that special, so it broke from impact.
Grabbing the barrel of the gun, I lifted your mother arms upwards, and she emptied the entire mag into the roof. Ignoring the look of fear and horror on her face, I lifted the broken knife and jammed it into the side of her head and watched as her eyes rolled to the back of her head. It was finally done. The threats were all taken care of, and we were now safe. Taking all their bodies downstairs and sitting them onto the couch, I ripped the bow ties of the presents they got you and tied it on their foreheads. After that, I got a chair and sat down in front of them waiting for you to wake up. And once I felt your presence in the back of our head, I lifted our arms up and screamed HAPPY BIRTHDAY MARVIN.