One thought can make one become an immortal, and one desire can lead to a demon. Immortality and demon are just a matter of one thought. Immortals must be good, and demons must be evil. If you are dedicated to good, what is the difference between the right path and the evil path? This article tells the story of the love-hate relationship between the cold demon brother and the gentle immortal brother. This article is my first time writing. If there are any shortcomings, I hope you will bear with me and give me more suggestions. I hope you all like it, thank you.