Mukuchi na Kare ga Zangyou suru Riyuu

Twenty-seven-year-old Risa is working at an advertising agency, pursuing her career dreams and forgetting about love. One day at the office, she nearly falls over carrying a heavy load! At that moment, someone unexpectedly extends a hand: Maruyama-kun, who joined the company at the same time as she. Although he is taciturn, expressionless, and unsociable (though actually quite handsome), when she glimpses his kindness, her heart skips a beat. Moreover, whenever she works overtime, she invariably runs into Maruyama-kun...

(Source: Starts Shuppan, translated)