NinjaDefenders does not allow the creation of duplicate nicknames.  

Please set a non-duplicate nickname, If you want to change your nickname in the future, please refer to the following instructions.  

■ How to change the nickname 

1. click the [Profile] menu on the top left of the screen → tap the [🖊] pencil-shaped icon to the right of the nickname 

2. click the [≡] menu on the top right of the screen → tap [⚙] Settings → click [Change account ID].