This Anti-Demon Ninja Is Too Serious

Travel to a world where demons are rampant and become an anti-demon ninja who executes justice. There's certainly nothing wrong with that. "I'm a serious person." Chu Xuanyi said righteously. "Mr. Chu, there are enemies." "Ah, look at my secret: Millennium Killing!" Thousand-Year Kill is also a ninjutsu, right? … This book is a fanfic of the mobile game Action Taimanin - but it only draws on the world view and a few characters. Please don't cue other works. I don't know the author at all, so please don't contact me casually. Any similar plot is purely accidental. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.