Originally Posted by AzureWinter

That last boss on ?-8 is really kicking butt. Even the best helper squad I can get rarely beats it.
Any advice for 3-starring this one? How much attack power is needed for that final boss?

What's your highest level girl? Your helper's level is capped at your highest level so that is probably limiting the power of your allies. You could have a level 70 helper but if your highest level girl is only 40 then they will be much weaker.