18+ Akarui Sekai Keikaku

To counter the declining birthrate, the Japanese government chose one high school to initiate the "Bright World Project." The rules are simple: during the span of a summer break, each student has to find a date... or face death. While 99% of the school formed relationships, 9 students remain. These 9 students will have to face this DEATH OR LOVE game, whether they like it or not!

(Source: MangaHelpers)