"It's not very common. Perhaps one in hundred sensor types does it. Mostly if they teach themselves some of their skills. If they have an experienced sensor to teach them it normally doesn't happen. Tsunade Sama found this anomaly during the second shinobi world war because one on her team had that immunity to genjutsu and she wanted to know if it was possible to teach it to others." Arata said.
"Okay, this is good to know. Well, I guess we will have to postpone the genjutsu test as it is not possible for us right now to test if Dark Phoenix can break genjutsu. Perhaps when it becomes more pressing I will let Kurenai test him. Just to satisfy my curiosity. What is your strongest genjutsu?" He asked Naruto.
"Illusion Art: Infinite Darkness." Naruto answered.
"Isn't that a jutsu of the Nidaime Hokage?" Arata asked.
"It is. We will have to talk about how you learned that jutsu, Dark Phoenix. For now, I think it is time to examine your ninjutsu. I would like to have a presentation of five of your strongest jutsu to see what you can do and then you will fight against Asuma." The Hokage ordered.
"Can I have an oath that nobody talks about those ninjutsu? I trust you that you chose trustworthy people to watch this test, but two of my jutsus will tell them exactly just who I am." Naruto said.
The Hokage was surprised at that request. Could Naruto know his father's most prized techniques?
"Okay. Arata, Asuma, if I am right about which jutsus Dark Phoenix intends to show us, that oath will be necessary. I make it an S-rank secret to keep quiet about them until I give you permission to talk about them."
"Understood." Both said.
Naruto nodded and took out a tri-pronged kunai from his pouch on his back. He threw it at the training post and vanished in a flash of yellow, reappearing at the kunai and showing a blue spiralling orb into the training post.
"Rasengan." He said and showed the ball through the wood as if it was butter.
"The Yondaime's jutsus." Arata said shocked. "Flying Thundergod and Rasengan."
Asuma gave a very good impression of a goldfish. He never had even suspected that the Yondaime could have had a son. That seemed to be the only plausible explanation for this boy to know those jutsus.
Naruto flashed back to his original position and went through a series of handseals.
"Water release: Water dragon bullet." He said and manipulated water from the river into a water dragon that hit the training post which already had a hole from the rasengan.
The post was blown away from the powerful jutsu. Naruto waited until the water had settled down and went through his next series of handseals.
"Wind release: Twisters' fury." He shouted and made three tornados that blew towards the river and sucked up the water making them even more dangerous.
Then Naruto made his last handseal.
"Shadow clone jutsu." He said and created fifty shadow clones.
"Shit." Was Asuma's only comment.
The Hokage was very impressed. He wouldn't have thought that Naruto had that kind of strong ninjutsus in his repertoire. He would be a force to be reckoned with in the future. This only made it more imperative to keep the boy in the village. He needed to choose a good jonin sensei with whom the boy could bond. It was only one real option there. While Naruto would only stay a genin for six months with skills like his, those months needed to be used to start positive bonds to the village. He couldn't take care of that through his team-mates, he would be paired with Sasuke Uchiha, Naruto had said himself he had intended to do that to make sure the team passed, and Sakura Haruno. He hoped it would be okay, but perhaps he should ask Naruto about his opinion about Sakura first. He didn't want to anger him even more than he already was.
The following fight with Asuma showed that Naruto had a wide range of ninjutsu he could use. Especially his use of replacement and body flicker was fantastic. Asuma didn't manage to get a hit in as Naruto changed places so fast. Together with his speed he could honestly say Naruto was high jonin level in ninjutsu. He knew how to do the jutsus and when to use them in a fight.
Finally he gave both the signal to stop.
"Damn it. To have to work like that against a kid his age, I really should start training more." Asuma commented.
He had been spammed with clones and tricked by transformations. Mixed with the constantly moving Naruto and his higher level elemental jutsus, it was damn hard to get the kid. If he would use his other skills Asuma didn't doubt he would be able to go up with jonin in a few months of real missions. He had noticed that while the kid was good, he made mistakes that someone who had been on a hundred missions or so wouldn't make. This meant this kid was a rookie. His opinion rose even more after that revelation.