This is the 2nd currency you will be introduced to in the tavern. It is available from level 1 and used until level 80. You can obtain this currency from playing Purple Soul Janken and getting top-up. You can only gain access to these currency if you are VIP 1 at minimum.
These are the ninjas that you can recruit with this currency
You also require this soul when upgraded these ninjas
For more information about other types of souls, please look at Souls