Feiyun took a deep breath, and a mass of clouds appeared behind him.
Dark clouds.
They seemed to be cast from black steel.
To onlookers, they appeared more like masses of steel rather than clouds.
Yet their shape was, unquestionably, that of clouds.
"Ninja Spirits of the natural element!"
Ling Xiao frowned at the sight of the dark clouds, sensing that Feiyun was even stronger than Feimu had been. Even with his Cherry Tree Martial Spirit, he wouldn't stand a chance against him.
"Indeed, Ninja Spirits of the natural element! And it's the most powerful kind!"
Feiyun declared proudly.
Like Martial Souls, Ninja Spirits are categorized into natural, animal, plant, and transcendent elements.
There is no consensus on whether the natural element is the strongest, but usually, below the Transcendent Realm, it could be considered the most powerful.