A/N All Harry Potter characters are the sole possession of JKR, not myself. This story takes place in their 6th year and is made up solely of my imagination.
Sirius moved restlessly on the bed in his cell. He had one threadbare blanket and almost no pillow. They had both wasted away after the nine years that he had been in Askaban prison.
No contact with anything human. At all. The Dementors came by every few days and took all happiness away.
He was bored. Very, very bored. He needed company. Now.
As he thought this, a Dementor came by the door to his cell. On impulse, Sirius grabbed hold of its robe and stopped it.
"Play with me!" Sirius demanded.
The Dementor looked at the hand holding its robe and then at Sirius's face. Sirius could feel its confusion. Nobody asked them to stop. Nobody.
Sirius picked up a piece of stone and drew a 3 x3 cross-hatch on the wall. Then he marked an "x" in an empty space. Sirius handed the piece of stone to the Dementor. "You need to mark an "o" in one of the spaces."
The Dementor hesitantly took the piece of stone and stared at it. It -didn't know what to do.
Sirius moved its sleeve to the cross-hatch and showed it how to draw on the wall. The Dementor looked at Sirius's face and drew an "o".
Sirius then marked an "x" in another open space, then indicated that the Dementor should mark another "o". The Dementor stayed to finish the game with Sirius.
After playing three games of tic-tac-toe with Sirius, another Dementor came by. Somehow it communicated with the first Dementor and held its sleeve out for the stone.
As word spread among the Dementors they, one by one, came to play the game with Sirius.
Sirius, by this time, was no longer bored. He did, however, wish that they would go away. He needed to rest. By pantomiming, he indicated that was what he needed to do. The Dementors didn't want to stop. Nobody had ever wanted them around before, let alone played games with them.
Finally, Sirius grabbed his pillow and blanket and moved to the far side of his cell. He laid down and wrapped the blanket around him. Once he was settled he shifted to his animagus form. Once he did that, the Dementors could no longer sense him.
After standing around for about 15 minutes, they all went back to their rounds. But instead of extracting someone else's feelings they had some of their own.
For the next year, every time that Sirius was in his human form, he found Dementors standing outside his cell door wanting to play tic-tac-toe.
At one point, he acknowledged to himself that this was the best prank he had ever done. He just wished that James and Remus knew about it.