The Big Black Blob.
It was the night before he would fake his own death. Aizen was writing the final letter to go to Hinamori. In a moment when her mind was filled with confusion, with a warning from someone she called "Shiro-chan".
Sweet Hinamori, Loyal Hinamori. He looked up to hold eye contact as he spoke to her his "final words".
After the conversation she eventually fell asleep.
Alone at last, Aizen looked down at his "farewell letter" only to realize that there was a big black blob in the middle of the sheet of paper. He would have to start all over.
An: This drabble was inspired by a Bleach marathon when we were watching the scene where Aizen was writing the letter while talking to Hinamori. My sister noticed that he was holding eye contact with Hinamori while his brush was still moving. This was a theorized idea on what happend to that sheet of paper.