The Butterfly Villain Is Skilled at Casting Gu

[Novel Blurb] -- I hear the young people of Miaojiang are experts at bewitching people's hearts. Brother Lan Wu, can you do that too? -- I can use Gu, but I can't bewitch people's hearts. -- Then why is my heart all in a muddle because of you? -- Because... I put a love Gu on you. Ye Yuan was once a fox who had cultivated for five hundred years. One day, she finds herself inside an old-fashioned, melodramatic tragic romance novel, as a mentally disabled young woman whose mind is stuck at age nine and who calls everyone "big brother." As the second most evil villainess in the book, she is supposed to marry the male lead on the same day as the heroine and become his secondary consort. She seems like a sweet, simple-minded white lotus, but spends every day tormenting the heroine. And now the System wants her to save a young man from Miaojiang who covets his brother's consort and puts a love Gu on her?! Uh, is this what they mean by two negatives making a positive? The villainess has to save a yandere villain?! The first time she meets him, he's playing with a blue butterfly. When she reaches out and asks to play with it, he teases her, "I'm afraid not, unless... you marry me." Ye Yuan: ??? Only later does she learn that touching his butterfly really does mean she has to marry him. Because it's a butterfly Gu he raised. When their marriage is decreed, he mocks her mercilessly: "Hah, so you really want to be my sister-in-law? A lowly secondary consort is enough to make you this happy? You're such a fool!" Before the wedding, he grabs her and pours out his feelings: "Why can my brother have you, but I can't? Whatever he can give you, I can give you too! Even more than he can! Come with me!" She has no choice but to refuse. The plot won't allow it. After she refuses to leave with him, he suddenly smiles again and asks, "Do you think my butterfly is pretty?" "Pretty." "Then can I let it rest on your hand for a while?" "Sure." [Beep. Host, the villain has planted a butterfly Gu in you.] Ye Yuan: ?! He pushes her away with an evil grin. "All right, now you can go back and marry my brother." "I wish you a perfect match and a happy marriage that lasts a hundred years. Oh, and on your wedding night... don't miss me too much." Later, she asks him to remove the Gu, but he says, "Sister-in-law, early spring hasn't even arrived yet. How could the apricot blossom have climbed over the wall already?" Reading Guide: 1. Both leads are each other's only partners, one-on-one romance, happy ending. 2. Romance-focused. Please note: this isn't purely sweet. The romance is bittersweet, and there are angst-filled parts in the second half. This story caters to a niche taste, so please move along if it's not for you. 3. Thanks to bs Gugu for the cover art. 4. For an explanation of the original heroine harming people at age nine, see the author's note in Chapter One. Theme: The stars don't ask how far you've traveled, and time rewards those with a devoted heart.