Agasa-kun wa Yandeiru.

"Please go out with me. I'll die if you reject me." Suddenly one day, Nanako Ichigotani is confessed to by Yuki Agasa, her club junior and the school's genius prince. Surprised by the sudden confession, Nanako, an airhead, says: "It'd be troublesome if you die!" and decides to go out with him. The clingy Agasa-kun, who is both unusually obsessive and possessive, has no mercy for any interlopers who get near Nanako!! A blind-love school comedy about an obtuse airhead girl and her yandere boyfriend!

(Source: Bunkasha, translated)