The Demonic Tuna, along with the Godfish are both very difficult to catch. Players are advised to continue putting stat points primarily into Focus. If Focus is maxed out, players may add more points into Intelligence and Dexterity.
This alone will not be enough. Players are strongly advised to craft their own fishing rods through the Carpenter life due to the rods being of higher quality when crafted. Upon reaching the Expert rank Carpenter, players may place an additional ingredient into their crafts. Some advisable ingredients would be a Soul Stone, a Soul Stone +, or a Giant Scale. The special effects of these items may be found on the Crafting Effects page.