That Genius is Obsessed With His Fake Girlfriend

"From today, we're adding a 'lover contract' to the mix." After discovering her boyfriend's infidelity and facing harassment at work, Hoshino Rin, nearing 30, found herself single and jobless, on the brink of despair. Her attempts at finding a partner through matchmaking were ruined by the intrusion of a mysterious, insensitive man. Then, one day, Rin agrees to do housework for a "brilliant programmer who lived abroad," at her brother's request. She assumes it will be fine since he's her brother's friend, but the person who shows up is completely unexpected...! A doting love story begins between a solitary genius programmer and a kind but unfortunate woman, starting with a contractual relationship!

(Source: BookLive, translated)