Goodbye Eden (also known as Sayonara Eden ) is a dystopian, post-apocalyptic manga by Zero Ainan
The series is a set in a world where scientists created a drug to turn the fear of death into pleasure. Chapter 34 Summary — East of Eden by John Steinbeck
Without giving too much away for those catching up, the main protagonist, Yuki, finally discovered the "Garden's Core"—a bio-mechanical heart that controls the simulation. Just as she reached out to touch it, a character we thought died in Chapter 12 reappeared, wielding a syringe filled with a black fluid.