Jinti

[Hero-complex ambitious heroine x obsessive, scheming, lovesick hero]

[Double mad characters / extreme push and pull / scheming against each other / pathological symbiosis]

Since they're both rotten to the core, they might as well sink together into this lightless abyss and fight to the death.

"He thought he had found the only light and offered up his soul in devotion, never realizing that at the end of that beam of light waited a demon, ready to drag him into eternal ruin."