This is a story related achievement which will come once you beat the 2nd boss of the game "The Crab" at the sanctuary.
The boss has around 700-800 health and can deal out huge damage!!
He comes with 2 little Amoebas which have about 40-50 health.
He has a drop attack which causes around about 100-120 damage to each character so watch out!!
The easiest way to defeat this boss is to use Edessot as a gather battery to gather and send it to Hoston (Your main attacker) and use Healing with Alina and Mohu.
If your in good shape I suggest using an attack or two with the other characters.
If your health drops below 120 heal ASAP!!
Once you beat the boss you'll be rewarded with the achievement!!