He Forced Me to Rob the Protagonist of His Luck

After traveling through time and becoming the most powerful young master of the first imperial clan of the top celestial sect, I decided to enjoy a luxurious life with overwhelming power. According to the original work, I will torture the child of fate in the most cruel way and rob him of everything. Until I heard the system whisper in my ear: "Congratulations to the host, you have successfully robbed the protagonist's 'beloved little junior sister' of related luck!" I was stunned. Wait, there seems to be something wrong with the victim in this mission description? The protagonist is myself, so who am I robbing now?