Heaven's Lost Property the Movie: The Angeloid of Clockwork

A short flashback of what happened in prequel of Heaven's Lost Property series until there's an Angel, Hiyori Kazane who is dreaming while her real body is in heaven. She had a crush on the main protagonist, Tomoki Sakurai who fight until the end where the world has memory about Hiyori erased when she died in her dream and returned to her real body. She wanted to return to her dream so much that she got modified into an Angeloid of Clockwork by heaven's master but got back consciousness with help of Tomoki. However, it was not enough to save her life.

Synopsis from Anime News Network