Starting with the Mangekyō Sharingan, I Enter Demon Slayer!

The protagonist wakes up and becomes Uchiha River, and by chance enters the world of Demon Slayer: Kimetsu no Yaiba. Ding dong! Congratulations to the host for achieving the achievement of genocide and being rewarded with a pair of Mangekyō Sharingan. "Since you guys don't have martial ethics, don't blame me for being ruthless." Uchiha River smiled evilly, and the coffin in front of him opened with a bang. "What do you think of life?!" The man in red clothes waved his blade. "I admit that human potential is stronger than ghosts." The proud Yiwuzao lowered his head. "Please, I will never eat people again..." Tong Mo, who had never felt fear before, clearly felt the threat of death. "Thank you for letting me know my brother's thoughts." Jiguo Yansheng's six eyes were filled with tears. "Who are you?!" Ghost Dancer Muzan looked at Uchiha River ferociously. "I... Am naturally the one who controls everything by destiny!"