Hitler of the Phantom

The girl disappeared for four whole years and was believed to have died at the claws of the monstrous beasts. At the offshore base called Xite, she reunited with her brother, who had all the makings of a harem protagonist... And yet his expressionless little sister was trying to build a harem for him?! "Brother, for the sake of your future bedroom life, practice running fifty kilometers every morning, then do forty thousand squats, and finish with ten thousand push-ups until you punch through the floor."