To get Soul Cane in King Legacy, you must defeat the boss Sally (Level 3450) at Pirate Skull Island in the Second Sea. While the quest to defeat Sally has a level requirement of 3525 there is no requirement to fight the boss and obtain the drop. Soul Cane is an Epic Sword, so its drop rate should be around 1%.
Soul Cane is one of the best swords in King Legacy, especially considering how accessible it is. Its M1 attack speed is fast, and it deals 1,801 damage with Armament Haki V1, but its main strength is in the two skills it provides as both can freeze the enemy, while the first move is great to break Observation Haki, thanks to its seven hits.
Its Z key move, “Icing Pierce” is unlocked at 1,000 Sword Stat Points, and it deals 10,729 with Haki if all seven hits land. The move creates an icy path in front of the user as they lunge forward and traps the enemy in an ice crystal. All that seems to be required for all hits to land and for the enemy to freeze is for them to be within the icy path, so the timing and aiming is much easier than Pondere Blade‘s Fling Rushes.
Its X key move, “Freezing Carnival” is unlocked at 2,000 Sword Stat Points and it deals two hits for around 2,715 damage each (6,780 total damage with Armament Haki). The move's range is really short as it creates an icy circle around the user, but it is great if used correctly as it freezes the enemy.
Note that you must have Armament Haki enabled for both Skills to work on Logia users.