The Curse of the Fireflies

Yao Yu inexplicably transmigrates into the Dream Realm, where she nearly falls victim to demons before being rescued by a mysterious man. To find her way home, she seeks out a fortune-teller. The answer turns out to be that she is merely cursed to catch a firefly, but an earth-shattering conspiracy soon comes to light! The firefly she must catch is actually her elder sister from a past life!

Over a thousand years ago, she and her elder sister both fell for the same man. He chose Yao Yu, and her sister held a grudge. In the end, a joyous occasion became a tragedy: after murdering Yao Yu, her sister killed herself in bitterness, and her soul became a demon...