Junior Sister Is the Savior, and I Am the Big Devil?

"What? You said that in the near future, the world will be destroyed, and I will be the savior Lord? "Gu Moying looked at the girl in front of him in shock. "No, you are just the savior's senior brother." A certain saint replied truthfully. Gu Moying: ..."Then what are you asking me for?" "Of course I want you to urge your junior sister to practice hard." "I see." "Then, do you need my help when you defeat the big devil?" "It's up to you."...· Looking at the girl in front of him, Gu Moying silently closed the "Strongest Devil Development System" panel. What you want to defeat is the world-destroying demon. What does it have to do with me, Gu Moying? Department? This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.