Surrounded By Insanity

Waking up in the middle of a city filled with rivers of blood, missing most of his memories of the past 10 years, with only the message in the sky saying "Do your best to amuse me.", Ubel Achlys has to do his best to survive and find out what happened in the 10 years he lost his memory, who exactly left that message in the sky and why did they possibly erase his memories.