Kanojo ni Norowareteru kedo Shiawase nanode OK desu☆

Being kind to girls is the most important thing to 17-year-old Harunari Iida. As the kind of guy to carry the bags of all the girls in his class with him to school each morning, those around him sarcastically called him the "Ultimate Gentleman Iida." One day, he encountered Sari Kageura, a beautiful girl with a strange aura, but he noticed a cursed-looking monster emerging from her body. Iida was going to hurry and flee, but wasn't something amiss...? He was cursed by the heroine?! A new sensation horror romcom!

(Source: COMICSMART, translated)