There is one rule.
For a wandering spirit, Gilbert didn't go very far. He couldn't really go very far; anytime he considered leaving town, something called him back. It wasn't the house – he could leave it easily enough. No one took up residence in it, though, after his accident. So he could stay there without being bothered.
He wasn't sure why he was still here. Something tethered him to this world still.
Just one rule.
He'd lost track of time, but it was the same season as his accident so many years ago when Matthew moved in. He knew that was the blond's name because another blond, a louder one Matthew called "Al," had come to help him unpack, and called his name into the house several times. And then Al was gone and Matthew was almost all alone.
Only one.
Gilbert spent days watching Matthew. He'd linger in doorways though he knew he wouldn't be seen, watching the man go about his daily business, such as cooking dinner. Slowly he grew braver, venturing closer. Matthew started to sense his presence, often looking over his shoulder, or staring straight through Gilbert with a look of mild confusion. He had violet eyes.
You must never forget this rule.
Matthew got a job and started getting up early and leaving on his second week in the house. At first Gilbert didn't even realize. The first day he assumed Matthew had run out of something for breakfast and went to the store. He didn't think too much about it when Matthew returned much later, without bags. But it happened again. And a third time. It was only then that Gilbert remembered the importance of a job. A job meant money for the food one needed to survive. A job also meant that Matthew spent less time in the house. For once, the isolation from all humans was not enjoyable. So Gilbert began following Matthew, walking beside him every day to the animal shelter. The silence between them was comfortable. Gilbert liked it.
Your very existence in this world depends on it.
Gilbert had a guess as to how he became a ghost, but it was only a guess. He remembered his accident with burning clarity. The pain, one of the few things he could still feel if he thought back. The fear. He remembered what happen next; the existence that came to him, that told him where to go from there. Something tethered him here – there was something he hadn't done, something he needed to do. He pondered for ages, obsessing over it, going over every detail of his life, and all he could come up with was his best guess.
Your tether...
Matthew brought home a cat one day. It was the size of a small dog and so fat Gilbert was amazed its feet touched the ground. Its fur stood up whenever it saw him, and it loved to get in the way. Matthew called it Kuma. Gilbert called it Little Shit. Matthew often moved when Little Shit's fur stood on end while it was sitting in his lap, and that damned cat would smirk at Gilbert as Matthew moved away. The longing to be close to Matthew, and the inability caused by Little Shit made Gilbert realize that he'd developed feelings for his housemate. Powerful feelings, so strong they terrified him.
You must never fulfill it.
Little Shit tried to kill Matthew. The blond was bringing laundry down from his bedroom to the laundry room when the massive beast came rushing past him, tripping him. The world seemed to freeze as Gilbert saw Matthew's eyes widen, his glasses slipping up his nose and his hair rushing backwards before one of the shirts in his arms flew up against his face. Flashbacks of his own accident, his fall down those very stairs, rushed into him, and for a moment Gilbert almost believed he had a racing heart, almost heard blood pounding in his ears, almost smelled the adrenaline and the fear. He rushed forward, catching Matthew before the blond could fall and meet the same fate. Matthew stared right through him, his eyes even wider while Gilbert straightened him up. He stared back, watching the other raise a trembling hand towards him. He reached his own tentative hand forward to meet it. Matthew yelped and nearly fell down the stairs again.
If you do, you'll move on.
Gilbert's best guess as to why he was there, his only guess, was that his tether was something he had yet to experience. A trust filled, entirely consensual love for someone; a love that didn't end in heart break or tragedy. Matthew moved out three days later. Gilbert could only smile joylessly and thank whatever gods of irony there were that his love was unrequited.
And you don't want to know what comes next.