Yuna Tachibana thought she knew everything about her boyfriend, Ren Kurokawa—until one day, he started acting like a completely different person. Sweet, caring, and strangely familiar, he knew everything about her... yet the Ren she loved never did. As hidden truths, identical twins, and painful secrets begin to unravel, Yuna is forced to ask herself one question: Which one was you?

Crimson Oath is a yakuza romance light novel that blends romance, comedy, action, mystery, and suspense.The story follows Aoi Mizuno, an ordinary college student whose life changes after an unexpected encounter with Ren Kurogane, the young leader of the powerful Kurogane Clan. What begins as a strange accident soon turns into a contract marriage, pulling Aoi into the dangerous world of the yakuza.As the two spend more time together, hidden secrets, betrayals, and a deadly conspiracy begin to surface. With danger closing in from every direction, they must decide whether to protect the clan—or each other.Filled with emotional moments, lighthearted comedy, thrilling action, and unexpected plot twists, Crimson Oath is a story about loyalty, sacrifice, and finding love in the most dangerous place imaginable.