In the anime, Rem didn't die. Why don't others remember her?

Answer 1

In the anime " Rem: Life in the Other World from Zero ", Rem did not die but was imprisoned in the prison of the Other World from Zero, so no one else had seen her.

Rem was a powerful Magician. She had once lived with Ange and became a powerful Magician with his help. However, Angor betrayed Rem and locked her up in a prison in the foreign world. Since Rem was imprisoned in prison, no one else had seen or heard of her name.

The reason why no one remembered Rem was because she was imprisoned in prison and was not publicly displayed, so no one had seen her before.