Its in-game description reads "Legendary sword. All but forgotten." This sword is effective for taking out rats, or beast-type enemies, because of its high Beast stat. It is also effective against undead monsters with its Exorcism stat. You can only find the Brave Ark in dungeons' chests, it cannot be bought or invented. This sword is a medium-tier weapon (Tier 5) : it'll gain 4 Synthesis Points per level-up.