Angel Beats!: Heaven’s Door

The light novel is the official prequel to the anime series. It tells the story of how Yuri and Hinata meet, how they find out about "Angel" and the other characters and how the SSS was founded.

Kanade Tachibana is a beautiful girl known as "Angel-chan" at school. She is traveling all over the country in search of "someone." One day, while staying in Kanagawa, she met Yuri Nakamura, a happy and cheerful girl. Along the way, other people who look like SSS members (?) also appear!? Will Angel-chan be able to find that special "someone"…? (Source: Kadokawa, translated)