Kimi to Aoi Yoruno

In Kimi to Aoi Yoru no readers themselves take on the role of the characters in the story and play out the story using a companion site. The story begins three weeks after the mysterious disappearance of Rino Tsunamoto, a high school girl, when four classmates secretly gather at school at night to try to solve the case. Readers take on the role of these four high school students as they try to get to the bottom of the "Rino Disappearance Case."

(Source: Natalie, translated)