Reincarnated Demon Princess, Heaven's Chosen Ones, Prepare to Die!

(Falling into depravity, becoming corrupted, gradually assimilating with an evil consciousness, lying low to take revenge, and ultimately turning things around.)

Yu Lian was murdered without remorse by a vicious young lady, then unexpectedly merged with a Demoness. Ten years later, when humanity broke through the Demon King's castle, the Demon King sent the Demoness back ten years at the last moment, ordering her to kill humanity's chosen heroes and prevent the Demon King's defeat.

Her human consciousness tries to stop her from harming people. But the Demoness's consciousness has her cheerfully singing the Demon King's praises as she gleefully drives a wedge between humanity's chosen heroes.

A scheming servant, a two-faced flirt, a conspirator: as she constantly changes roles among humans to sow discord, can she still hold on to her human heart?

"A dazzling butterfly will never yearn for the self it once was as a caterpillar in its cocoon. I, the Demoness Meisiphlada, swear to fulfill the Demon King's every wish, even unto death!"

"But you haven't killed a single person."

"What?"

"You actually love humanity, don't you?"