Sirius Black has one rule: don’t fall for his twin sister, Y/N Black. Marlene McKinnon breaks it without meaning to. What starts as harmless friendship slowly becomes something far more dangerous—lingering looks, quiet concern, jealousy she refuses to admit, and a growing emotional dependency she can’t explain away. The problem is not just that Marlene is falling for Y/N, but that Y/N is also deeply attached to her in a way that feels like it could become love at any moment. The real complication is Sirius. He notices everything. And he is not subtle about his protective instincts. As Marlene tries to hide her feelings, the situation spirals into a mix of suspicion, jealousy, accidental almost-confessions, and tense moments where Sirius begins to realize something is changing between his sister and one of his closest friends. Meanwhile, the entire friend group watches the disaster unfold, fully aware that this slow-burn romance could either become something beautiful—or blow up the Marauders’ entire dynamic.