It is not possible to create a duplicate nicknames in Idle Berserker. 

If you want to change the nickname, Please use the nickname change ticket.

 

■ How to purchase a nickname change ticket

 - You can purchase it using Guild Coin in the Guild Shop.

 - Guild coin can be obtained from guild attendance, guild mission, etc. Please join the guild.

※ How to join a guild : Click on the Guild icon at the top right of the screen