Transmigrating into a Book to Become the Demon Lord Heroine's Junior Sister

(Dual female leads + somewhat slow burn + tragic ending + System + both leads are each other's only partners + faked death) New book just launched. Please show it lots of support. Stick with it and it'll definitely amaze you, dear readers. Adorable secret-identity junior sister × once-brilliant, aloof senior sister Su Yue transmigrates into a female-led novel. As a transmigrator, her task is to save the heroine in the early part of the story and build a deep emotional bond with her... After successfully winning her over and returning to her original world, just as she is about to embrace her new life... “Nuo'er, how could you leave me behind?” Su Nuo looks horrified. “Why are you here?!” “Of course I came to find you, Nuo'er!”