well you may know how to farm levels, but by the time you get to the farming point it'll already be late game so meh.
Also, yeah, make one of the generally op personas like satanael, or yoshitsune. You need two things imo:
No weaknesses on akira, and high power as often as possible.
I did it after reapering until level 70 I think. ( maybe less.) At least enough to unlock all skills on team mates. Used the all girls team.
Makoto on healing and defensive buff as well as casting the occasional nuke.
Ann alternating between concentrate and that severe fire skill. I also had her matarunda the twins when needed.
And haru dishing out heat risers and psy stuff.
Joker did the same as ann with power charge and hassou tobi. Equip sp patches on everyone. and boom. It's a fight of attrition now. One only you can win.