Fujin analyzed, 'Hmm, not bad. With some practice, I will be able to freely control the shape and size of this blade. It can catch opponents off guard.'

Fujin decreased the length and instead changed the shape. Instead of a sword, the weapon now looked entirely like a Vajra. Fujin changed the sword's shape to various other shapes to find out its limits until he was satisfied.

He stopped experimenting with the sword and muttered, "Time to experiment with the main feature of the sword"

Fujin closed his eyes and recalled the training the Ame Jounin had gone through after he received the sword. Fujin knew neither the Lightning Dragon nor the Lightning Crow jutsu. Though they weren't difficult to learn, he decided to keep it simple and experiment with the False Darkness jutsu instead.

Fujin began sending his chakra into the Blade of the Thunder Spirit. He closed his eyes and began creating the False Darkness jutsu while using the sword as the medium. Soon, he opened his eyes and pointed the sword at the sky.

A large amount of Lightning was unleashed from the sword. It travelled towards the sky without any control. Fujin frowned and analyzed, 'It's difficult to control I have no control over the Lightning I released with the help of the sword Also, my efficiency was quite low. I lost nearly half my chakra while trying to create the False Darkness jutsu. However, with the 10 times amplification that the sword provides, the jutsu was 5 times stronger than what it would have been without the sword. It looks like I'll need to practice with this sword for a long time to increase my efficiency and control.'

Fujin let out a sigh. He had added yet another training to his already ridiculously tight schedule! Fortunately, this one won't need as much time and dedication as some of Fujin's other projects like the Flying Thunder God jutsu, the Wind Domain or the Eight Inner Gates Technique.

Fujin decided, 'Since Shadow Clones can have the Blade of the Thunder Spirit as well, I'll just create multiple Shadow Clones to practice. Due to chakra amplification, the clones won't need much chakra to practice anyway. I'll create 10 Shadow Clones with 1% of my chakra reserves and have them train while I meditate the entire five days and only replace the Shadow Clones after they pop.'

Fujin quickly acted on his plan. He created 10 Shadow Clones which began practicing, while he constructed a cave in the mountain and inscribed the seals to improve the efficiency of meditation like the room in his basement.

Fujin's clones continued training while Fujin only meditated and created new Shadow Clones when the existing ones got dispelled or ran out of chakra. On day 3, Fujin made a change. He stopped training the Rasengan Cannon and instead created 2 Shadow Clones with 30% of his chakra each and another two clones with 10% of his chakra each to work on the Rasenshuriken.

The reason for the change was that two clones with 10% of his chakra each were insufficient to create the Rasenshuriken! The clone infusing Wind chakra into the Rasengan needed a lot higher chakra to properly create it. Fujin was surprised by the amount of chakra he needed for the jutsu. However, on thinking for some time, he recalled that Naruto couldn't make many either until he learnt Sage Mode and got control of Kurama's chakra.

The training continued for 5 days straight before the effect of the soldier pill ran out. While he made huge progress, he wasn't satisfied. He rested for a couple of days before consuming another pill and continuing his training.

Three more days passed. Fujin was meditating in his cave when suddenly his eyes snapped open. He disappeared from the cave and appeared some distance away from a couple of his clones.

Two of Fujin's clones were focusing on their jutsu. One clone had created and maintained the Rasengan while the other clone was continuously infusing large amounts of wind chakra into the Rasengan.

When Fujin arrived, the Rasenshuriken was almost created! It was the best one Fujin's clones had created so far. Fujin and Kaito watched intently as the two clones needed another minute to complete the jutsu.

A smile formed on their faces as they managed to create a proper Rasenshuriken for the first time! The clone holding the Rasenshuriken looked at it and thought, '5 days to learn Wind Release: Rasengan and 8 days to learn the Rasenshuriken with just two pairs of Shadow Clones training! Excellent! Time to test it.'

He turned around and slammed the jutsu into the mountain they were training on. The Rasenshuriken sank a few meters into the Mountain. At the same time, the Shadow Clone's right arm felt the backlash of the jutsu and got dispelled!

The Rasenshuriken exploded a moment later. A large crater was formed on the side of the wall as it disintegrated into sand and soil. A tremor was felt throughout the mountain, scaring away any birds and animals living on or around the mountain. It took several minutes for the dust and soil to settle or fly away. If one were to look at the mountain, it would feel like a large monster had taken a bite of the side of the mountain.

Kaito, who had flown next to Fujin, said in amazement, "That was cool. What's this jutsu?"

While Kaito had seen the incomplete version several times, a complete Rasenshuriken was in an entirely different league. He could sense that none of the Winged Sabertooths could resist the dangerous jutsu Fujin had just created.

Fujin smiled and said, "It is called Rasenshuriken. It's a jutsu made with Wind chakra and a high-level chakra shape transformation. In terms of destruction, this will be the strongest jutsu that I know."

As he spoke, Fujin thought, 'That said, I still need more practice. Unfortunately, the amount of chakra this jutsu takes is ridiculous. Seeing the amount of chakra the two clones lost, I'll need 36% of my chakra for just one Rasenshuriken. It's just too much.

That said, it should be much less than what Naruto needed initially. It should be because I am much more efficient in infusing Wind Chakra as compared to Naruto who had just learnt Wind manipulation.

Though the jutsu sounds simple as I only have to infuse my Wind chakra into the Rasengan, it is extremely complicated. The only easy part is converting normal chakra into Wind chakra and releasing it. If control over wind chakra is bad, then a lot of wind chakra will be lost during the time the process of infusing chakra into it.

Even after infusing the wind chakra into the Rasengan, the clone that maintains the Rasengan has to ensure that the Wind chakra isn't lost and stays within the Rasengan. Even for me, I lost close to 50% of the wind chakra I infused into the Rasengan during these processes.

If my efficiency was only 20%, then the chakra I needed would have risen 2.5 times. So, it won't be a surprise if he needed several times more chakra as compared to me to create a Rasenshuriken of the same power. Of course, it also means that I can work towards decreasing the amount of chakra needed to create the Rasenshuriken by a large degree. At the very least, I should try to create at least 4 Rasenshuriken with my current chakra reserves.

Of course, that is only one part. I'm not a fan of needing a Shadow Clone to help create a jutsu. I need to work towards creating the jutsu without needing another Shadow Clone to help.

Apart from that, I also need to create a Lightning version of this jutsu. I shouldn't be able to create it with the help of the Blade of the Thunder Spirit due to the level of chakra shape transformation involved, but even without that, having a rank S jutsu that is so destructive is always helpful. However, I am not as used to using Lightning as I am with Wind. My efficiency will be a lot worse with Lightning. It could create some complications.

Another variation I want to explore later on is if I can add Fire Chakra to the Rasenshuriken. If I can, then the jutsu will be far more devastating than the Rasenshuriken. Sigh, so much to do again. Just when I feel that I'm heading somewhere, more training comes up.'

Fujin let out a sigh. While he understood the importance of training and strictly followed his training schedule, he couldn't help but get a sense of Fatigue. He thought to himself, 'No wonder there are so few ninjas who reach rank S. Despite having so much motivation, I'm still feeling tired. For normal ninjas, it is highly unlikely for anyone to maintain a strict training schedule for more than a few months.

Anyway, I should stay here for another week. Once I get a hang of the Rasenshuriken and Rasengan Cannon, I'll leave. I'll return later to improve it and learn the variants. Staying any longer here without informing Hiruzen about my absence won't be good.'