I was 70 when we first got it, but I was able to fini* at 100% HP using Tsunade, OTK Naruto and Kakuzu. Use your healing jutsu after AOE poisons and you're good. It's not really about power so much as how high you can combo. Strong Approching has 'Tough' enemies, which means they have two-digit HP but they only take 1 damage from attacks and heal to full every round.

Now to find a team that can kill Karin on normal difficulty...