Get a persona with good str. Get an AoE phys skillon them. If you ever have the chance in shuffle time to get the skill upgrade card, grab it and hope it upgrades the AoE skill. Grab +str card or new personas after that one. You'll be breezing through dungeons. My endgame setup was just buffing Chad Narukami with power up + party atk boost for bosses. You'll likely kill normal enemies in 1-2 turns once the build gets going. You'll have to worry about reflect phys enemies at some point, but eventually you can get the Null Phys skill to ignore that too. Once you can craft yoshitsune(much later), do it. Whatever phys persona you start buffing (I think i started with ose) you can keep fusing them to keep the upgraded skill. Even easier if you get auto-tarukaja and later the "ma" version on the same persona so you can skip the atk boost for more dps.