Kakashi sensed that he was about to witness an amazing technique, so he observed it with his Sharingan.
But when he saw that Eiji only blow air through his mouth into the atmosphere he began questioning Eiji's sanity.
Blowing air into the air seemed like the most chakra waste one could think of.
However, he quickly notices how the weather began to change.
This was because when warm moisture-laden air rises rapidly into the air, storms are formed. Sasuke used fire for that, but since Eiji is proficient in wind and not fire release, he directly used wind instead.
Now, to actually form Kirin out of a storm, you would need to be highly proficient at lightning release like Sasuke. For Eiji who didn't even bother to train other nature transformations besides wind, this was impossible.
For what reason did he then create a storm?
Because storms are a prerequisite for tornadoes to form.
Normally, air rising in thunderstorms begins to spin when it's affected by winds blowing it from different directions, but Eiji can just rotate the wind on his own.
Anyway, the storm Eiji was now fully formed and everyone finally realized that Eiji would use nature's chakra instead of his own.
What a genius and novel idea!
Unfortunately, the one who came up with this (Sasuke), would get his credit stolen by Eiji.
"Using nature's chakra...the jutsu we are about to see will be on a non-human level..." - Kakashi made sure to see every little detail with his Sharingan so that he might copy it.
"...this...damn it. Even after training 3 years with pervy sage, I'm still so weak compared to that..." - Naruto
"What a talented youngster...truly Konoha still is a shinobi powerhouse after all these years." - Chiyo
'...I never thought you could use chakra like that...' - Sakura
'Hmm...this looks pretty bad...he is more troublesome than I expected... let's just retreat, yeah.' - Deidara noticed that flying around when a strong weather-based jutsu is about to form, would be a bad idea, so he chose to escape.
There is no shame in retreating when you are a wanted criminal!
However, the strongest aspect of Kirin was the speed which made dodging impossible, but since Eiji didn't use lightning, but a tornado which wasn't as fast instead, was it still undodgeable like Kirin?
The answer was yes.
A huge hurricane started to form in the storm and everyone held their breath.
Not only was it a hurricane, but it had the shape of a giant tiger.
It was like a heavenly deity descended upon the world!
Deidara stopped his escape to gaze upon it.
And he started to laugh: "HAHAHA!!! AS AN ARTIST, I CAN'T HELP BUT ADMIRE THIS ART OF NATURE!!"
He seemingly lost his mind and continued to look at it like he was looking at an art piece in a museum.
However Eiji didn't care: with his yellow snake-like eyes which gazed solemnly at Deidara's figure in the distance, he closed his palm into a fist when the tiger was fully formed.
"Tear him apart, Byakko!"
The hurricane-tiger seemed to roar while traveling to Deidara's location and destroyed everything on its path.
It's speed wasn't really impressive, it was on the level of the speed of when Naruto throws his Rasen-Shuriken, but it didn't need to be fast.
Like Kirin, it wasn't dodgeable since Byakko made use of the characteristics of wind: even if he missed or Deidara tried to dodge, as long as it's somewhere around its traveling path, everything will get sucked in and then shredded into countless pieces.
Only if you have a way to increase your weight to an unbelievable level, could you manage to not get sucked in.
But like Kirin, Byakko was huge and could target a giant area, so hitting an opponent wasn't a problem at all.
In short, it was are truly powerful jutsu deserving to be classified as an S-class jutsu.
Deidara realized too late that he should stop gazing at this "art" and probably should try to dodge, but he could feel how he and the bird he was flying on was sucked into Byakko's "mouth".
"Shit...but dying to something as artistic as that, doesn't seem too bad, yeah..."