Phenomeno

Anyone who encounters Yoishi dies seven days later. Yoishi is not a living human. Any offline gathering she attends meets a terrifying end...

I—"Nagi"—have stumbled upon the beautiful girl, Yoishi Mitsurugi, whose legend is whispered about like an urban legend on the little-known occult website, Ikaigabuchi. That was the beginning of a story that shouldn't have ever been known.

(Source: Kodansha, translated)