Horrible Sign-In: After Death, He Became His Sister's Guardian Spirit

My name is Qin Ze. By the time you see this intro, I'm dead. By the way, I have a sister, She is very cute, very obedient, very well-behaved, very beautiful, very 'fierce'… I promised her that I would take care of her and pamper her forever. However, I broke my promise. I was killed... But what makes me happy is that After I died, I became my sister's guardian spirit so that I could be with her forever. I also got a system, The system said that I only need to kill weirdos to level up. When my level is high, I can better protect my sister, meet my sister, hug her again, and... Fulfill my promise to her! I have no choice but to break the truth for my sister! Regardless of whether you are a thousand-year ghost king or a thousand-year zombie, I will kill you in exchange for experience. Whether you are a terrifying evil spirit or a charming fox demon, I will... Ugh! ? Wait... Charming fox demon? If this, this... This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.