Riku, a university student, is left devastated when his long-term girlfriend is cruelly stolen by another man. His life hits rock bottom until he meets Yuji, a charismatic middle-aged man who takes Riku under his wing. Under Yuji’s guidance, Riku embarks on a total transformation, aiming to shed his identity as a “loser dog” and become the ultimate lion: a legendary playboy of the Reiwa era. Set against a contemporary Japanese backdrop of university life and the seductive underworld of romance and power, the story follows Riku’s journey through a harem of women as he learns to dominate social and romantic situations. His arc shifts from heartbroken victim to assertive, sexually confident king of beasts, navigating a series of encounters that test his resolve and reshape his identity. The narrative blends erotica with a comedic, seinen tone, chronicling Riku’s rise from despair to mastery.