Kowareta Bokura no Senryaku Renai

He seeks no ups and downs in life or in his emotions. He spends his days without any expectations, but then a beautiful girl, Saya, who is the complete opposite of him in every way, approaches him. She has it all: good looks, popularity, and happiness, but for some reason, she suddenly and unilaterally declares that she and Kento are dating. Moreover, she even kisses him...? The flat darkness is filled with swells and sparkles! For those of you who despair of the cramped world, Atsushi Uchiyama of I Can't Choose Between the World or My Girlfriend presents you a coming-of-age, big-bang read!

(Source: Kodansha, translated)