From MangaHelpers:

There existed a rumor in school about a secret murder club that killed people for you. All you had to do was write that person’s name on a red paper and tie it to a branch of a particular tree on campus and the murder club would do your dirty work for you. That rumor died years ago and no one thought twice about it until very recently. There seems to be a new generation of killers that are starting to make their presence known on campus and reviving the murder club. Not one person is safe from the deadly methods of the most dangerous club in history. [vyc]