Eiyuden Chronicle: Hundred Heroes

If you end up playing Eiyuden through the postgame it becomes trivial to get this achievement, especially since if you are going to do the old-fashioned grind for Nowa to Level 99 you will be routinely breaking this limit.

A party that will deal this damage nearly every time in the Endless version of the Hero's Trial only needs Momo, Leene (or Lam), and maybe Dijkstra (all around Level 70, all with fully-upgraded weapons). The key is to kit them out with the right runes, which unlock fully after I believe Level 60.

Momo:
- Rune of Conflagration (highest-level fire magic)
- Rune of the Mage's Pinnacle (greatly boosts magic attack when in back row)
- Rune of the Mage's Path (sacrifices magic defence to greatly boost magic attack)
All other available runes should be magic attack-boosting (Arcane Magic wherever possible)

Leene (or Lam):
- Rune of the Warrior's Pinnacle (greatly boosts physical attack when in front row)
- Rune of the Warrior's Path (sacrifices physical defence to greatly boost physical attack)
All other available runes should be physical attack-boosting (Tremendous Power wherever possible)

Note that Lam does not use AOE attacks like Leene, and she should be in her transformed state (use her Rune-Lens' MP-consuming power) if you aren't getting enough damage in a turn (both her transformed state's basic attacks and the transformation-ending rune-lens attack, Last Resort, hit much harder than her default state's basic attacks). You also can't arm both of them at the same time since there is only one Rune of the Warrior's Path available in a single playthrough of the game.

Dijkstra has a warcry that boosts the attack of all other party members for the turn. It may be necessary if you are short on damage.

Basic attacks (and Leene's SP attack) would probably be enough to exceed 3000 points of damage, but you can use Momo's fire magic to make up the difference as well.

Not really a guide, but a reference that may help. I got this by accident while fighting the Kraken in the Hero Trials. I had Momo in my party and I used Inferno Pillar (Rune of Inferno) which causes 1,100+ damage every time. This in combination with the other characters made it possible. I had Yusuke with 2-3 Charge-Ups and then used Rune of Armor Piercing for another 1,100+ damage. Iugo with regular Slash and Nova with Swinging Slash, and you can also put a weak character on the Crossbow (Gimmick). Make sure weapons are fully upgraded for all, and you should be able to get this.