Very Sincerely Yours (слэш)

Terrified at the prospect of humiliating himself in front of the ton and completely ruining his first season with his crippling shyness, omega Stiles Stilinski does the only thing he can; he invents a sweetheart away at war. A completely fictitious and utterly gorgeous captain, a gentlemanly paragon of romance and adoration, an alpha with whom Stiles spends years "exchanging" letters.
Years later, an angry, war-battered Derek Hale shows up at Stiles's door. He's no gentleman, and vehemently denies the existence of anything remotely resembling romance. He's received every last letter and has come to collect on Stiles's promises of home and marriage, no matter what.