Blood LoopRed ring, 赤环; Crimson Loop

Coming from the mysterious space, the Grey and Crimson creatures collide on earth. They are managing to transform as many humans as they can into their own kinds. Xiao Cheng and Zheng Yiren, best friends from childhood, were transformed into Red and Grey respectively. Standing on the opposite points, facing this collapsing world, what choices will the two brothers make?