A/N: This is kind of based off of the BtVS episode "Out of Sight, Out of Mind" but you don't have to see that to understand this. (However, if you have seen it you'll understand the title.)
Disclaimer: I don't own HP or "Out of Sight, Out of Mind."
The first time it happened was in my first year at Hogwarts. I still remember it clearly, the image vivid in my mind. Hmm, ironic. It happened in the Great Hall of all places, right in front of the entire school. But no one noticed. Not even Dumbledore with his twinkling all-seeing eyes. I suppose that was the way it was meant to be; after all, if someone had noticed, it wouldn't have been happening. Anyway, it was during dinner, I remember the pudding was quite delicious, when I saw it, or rather I didn't see. I was holding my spoon and then I could see my spoon. All of it. Right through my hand. My eyes traveled up where my arm would have been if it was visible, and I saw the last tinted remnants of my arm vanish as the color receded beneath my sleeve. I screamed and jumped out of my seat. After all, it isn't every day that your arm became transparent. Every head turned to me. I looked back to my arm, and I could see it. I quickly ran from the Great Hall.
My problem was obvious, and easily remedied. I became "Loony" Luna Lovegood. I started reading the Quibbler upside-down. I told everyone I encountered about my fathers wacky conspiracy theories. I wore kooky jewelry and perfected the dreamy, wide-eyed stare. That did it. People started mocking me, calling me names. Stealing my stuff became a house sport. I was knocked to the floor daily. My life sucked, but for a while everyone saw me, and I could still see me.
Then in my fourth year, everything changed. I made friends. There was the DA and Harry and Ginny and Ron and Hermione and Neville. They accepted me. So I toned down the weirdness. I didn't need it anymore. I was visible.
I didn't last though. My friends soon grew tired of me. Too bad I noticed it a little too late. Without my strangeness my housemates and the rest of Hogwarts ignored me, and then when my friends ignored me too…
The next time it happened was in my fifth year in the girl's bathroom. It was in the middle of class so no one was there. I was gazing at my reflection in the mirror. Little by little the colors faded. I was disappearing from the mirror, from everything. There was no use to fight it. It was inevitable. Why fight fate? I found it odd how I couldn't feel it. How I felt nothing as my body slowly disappeared from my vision. I waited a little while and then my clothes vanished as well. I was gone. I moved around a bit, testing my invisibility. I turned on the tap and put my hand under the water, an unseen obstruction to the flow of water. It was kind of cool. But I didn't want to live my live freaking people out with water tricks. No, the invisibility opened something in me. A need. But a need for what?
I finally realized what was missing when I accidentally pushed Pansy Parkinson down the stairs. I didn't mean to do it, I just wanted to frighten her, have some fun. But as she tumbled down the stone steps and landed, crumpled, on the floor, a pool of red spreading around her head, her eyes staring glassily at the ceiling, I found what I was missing. A surge of joy rose within me, a kind of satisfaction. And I laughed. People tending to the fallen Slytherin gazed around in confusion at the disembodied laughter ringing around them. I smiled wider. What fun invisibility was going to be!