It can be obtained by beating the Coliseum for the fourth time. While it can be equipped on Darius and his friends, equipping the Frying Pan on Darius would allow him to one-hit kill most enemies. Note that the attack animation for this weapon is quite slow, so the Frying Pan is best used on a character that does not prioritize speed.
The Frying Pan is one of the weapons shown in the early official screenshots released by From Software for Forever Kingdom, along with the Soltan Sword, the Seculian Sword, the Seculian Loops, and Zul's Toy.
One of From Software's early official screenshots of Evergrace II.
Frying Pans In Use
Early screenshot. Note the different character icons up top.