Angel Beats! The 4-Koma

In a world after death, angels fight for their fate and their future. Yuri, the leader of the Shinda Sekai Sensen, rebels against the god who destined her to have an unreasonable life. On the other hand, Tenshi, the chairperson of the student council for the world after death, battles against the SSS members. SSS members utilize armed weaponry to battle it out against the angels harnessing supernatural powers. Angel Beats! Heaven's Door is based on the the novel Angel Beats! Track Zero.

Angel Beats! -The Last Operation- will reveal why the Afterlife Battlefront members came into this world. New Angel Beats! manga series serves as the "true arc." (Souce: MangaUpdates)

A comic featured in the booklet joined with the CD "Last Song" of Girls Dead Monster starring marina, consisiting of two short stories: 1. Last Song, Yuriko Asami 2. The 4-Koma - Bokura no Sensen Shinoukyoku ♪ (The 4コマ 僕らの戦線行進曲♪); Haruka Komowata

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)

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.