After returning from the future, I claimed the realm's greatest swordsman—rivaling even the Prince—as my devoted younger brother. Though unbound by blood, I lavish him with unmatched tenderness and care. He serves a dual purpose: shielding me from my former fiancé whose treachery cost me everything in my previous life, and commanding our father's forces in battle. Yet darkness dwells beneath his devotion. "From the moment I first laid eyes on you, I never regarded you as family," he whispers, his gaze burning with possessive hunger. "My dearest sister." The dangerous creature I nurtured reveals itself through eyes alight with obsession.