Unfortunately my friend it really seems like it's all down to personal luck and how RNGesus decides to treat you. A lot of us here have started from Day 1 and have farmed either Dark Lord or the next area's Ninja Spy and have only managed one or none... and some have the full set. So don't worry too much about it xD
You're just gonna have to farm till you get lucky or use up kobans to do a 10 string super gacha to guarantee one of the girls.