Isho, Koukai.

Everyone in Class 2-D of Kairei Private Middle School receives an e-mail at the beginning of the school year detailing a "class hierarchy." But the number one ranked Tsubaki Himeyama clears away the unrest this causes with her sunny disposition. Normalcy returns to the class... until Himeyama is found to have killed herself on campus. And once her classmates return from her funeral, they find suicide notes addressed to them on their desks! Will these notes expose the darkness class 2-D conceals?!

(Source: MangaUP!)

Note: Includes 1 extra chapter.