Magical Girl Apocalypse

Magical Girl Apocalypse, also known in Japan as Mahō Shōjo of the End (魔法少女・オブ・ジ・エンド, lit. "Magical Girl of The End"), is a Japanese action-horror magical girl shōnen manga series written and illustrated by Kentarō Satō. It began publication in July 2012 in the manga magazine Weekly Shōnen Champion, published by Akita Shoten, and has been compiled into eleven tankōbon volumes as of April 2016. The series is published in North America by Seven Seas Entertainment.

A spinoff manga series called Magical Girl Site (魔法少女サイト) which has been published in Champion Tap! since July 2013. The anime adaption premiered on April 6, 2018, while licensed by Seven Sea.

Plot
Kogami Kii hates his normal everyday life and wishes for something to happen. One day in the middle of class, he looks out the window and sees his teacher’s head explode when a little girl hits it. He goes to the bathroom to calm himself, but when he gets back to the classroom, he finds most of his classmates killed by the same little girl.

Magical Girl Site
Aya Asagiri is a middle school girl who has problems with bullying, both at school and at home. While browsing online, a website pops up on her computer featuring a creepy-looking person. This person appears to take pity on her, and announces that she has granted Asagiri magical powers. Later cornered by bullies again, Aya fires the gun that mysteriously appeared in her locker earlier that day at them. The shot causes the bullies to disappear, but to her horror she finds out that they somehow had been hit by a train nearby. Feeling guilty and her appearance that themed with blood, Asagiri later finds that she is not alone, when a classmate reveals that she is also a magical girl who has offered her assistance. The two girls later learn about the magical existence, while wondering about something that looks like a countdown clock on the website, and fear it might be something bad.

Other Wikis

 * Mahou Shoujo Site Wiki - Wikia on the spinoff series.