One Day, Out of the Blue, I got a Gal's Forgiving Wife.

Synopsis

"Hey, why are you always pretending to be asleep?" Miran Hanazuki, the most popular gal at school, often calls out to him, the bottom-of-the-barrel otaku, Shuji Nagasawa. He was confused by her flirtatious attitude, and then she unexpectedly declares that she's engaged to be his fiancee!? The beginning of a romantic comedy between two polar opposites, an introverted otaku and an extroverted gal!! (Source: Kadokawa, translated)