Humans have advanced technology enough to be immortal, they conquered the universe, solved all of humanity problems and became god like creatures.. Of course, they got bored with nothing to do and one by one ended their lives. All untill one girl stayed, she was alone for thousands and thousands of years, when she suddenly saw new species getting evolved and starting their new civilization with their own rules, she was viewed as a "mythical being" that will kill everyone that gets close to her island... Hope that enough for someone to remember the title. If I remember correctly it was Yuri or at very least romance.. I hope I piqued your interest if you have never read it. Thanks in advance! -Cass