Ghost ; Base thing you have to do is increase girls active lv you need as high as possible (max is nice).
After that just like game said try to stack girls with activation rate boost into the group.
I think there is 3 type of activation boost now.
I believe Nutaku OP skill rate activation, compare to DMM side.

skasio ; It's should be compensation during manyu forging system failure.
250 manyus surely a lot.

game ; Go for your waifu man. Good luck.