18+ Yonhyakunijuu Renpai Girl

The "crushing heartbreak romantic comedy" follows Haru Tsuwabuki, a boy who must successfully confess his love to one of 420 girls, or he will die (in more ways than one). Haru is one of the few boys at St. Cinderella Academy, a "sanctuary" for exquisitely beautiful girls. However, as soon as he enrolls, he is derisively labeled a lowly "parasitic biting insect," and his adolescence descends into darkness. One day, Haru meets Miyako Dokuutsugi, a beautiful girl with the worst misfortune at the academy. Haru's life descends from darkness even lower into hell.

(Source: ANN)