Getting the Sturdy Helixhorn
You must find a Sturdy Helixhorn during the final quest of the “A Better Engine Blade” series to upgrade your sword to Engine Blade III. The quest can be obtained from Cid at Hammerhead outpost after you have completed the first two steps. Similar to Coeurl Whiskers, the Sturdy Helixhorn is only dropped from the Duplicorn monster type. It is an extremely rare treasure. To find and kill a Duplicorn, go to Cleigne: Old Lestallum outpost and talk to the Tipster at the diner. Tipster will give “The Last Spiracorns” Level 29 bounty hunt that requires you to defeat two Duplicorns and three Spiracorns at Lower Wennath. Sturdy Helixhorn is not a guaranteed drop from this quest — so you may have to repeat it multiple times to get one. To further increase your chances of it dropping, attack the Duplicorn’s head so a Sturdy Helixhorn is dropped and not damaged during the fight. Instead of repeating the quest multiple times (which is fine since it still rewards XP and some Gil), simply create a manual save file before fighting the enemies and keep loading it until a Duplicorn drops the Sturdy Helixhorn. Once the Sturdy Helixhorn has been acquired, return to Hammerhead and talk to Cid to upgrade the Engine Blade to Engine Blade III, maxing out its damage output. You will also get a decent amount of XP for completing the quest.