Ninjutsu is a type of Jutsu in the Naruto and Boruto Series. While Taijutsu does not rely on Chakra and Genjutsu relies entirely on Chakra, Ninjutsu is a mixture of both, since Shuriken Jutsu does not require Chakra but is considered Ninjutsu.
Apart from the Shuriken Jutsu, Ninjutsu is usually the manifestation of Chakra into real world effects. Most times, hand signs are required to be weaved in order to cast Jutsu as it helps mould Chakra in shapes and forms as required by the casters.
Kaguya Otsutsuki, the first person with Chakra on Earth could use Ninjutsu, although it wasn’t called that back then. Her son, Hagoromo Otsutsuki also possessed Chakra, which he tried to understand. He invented Ninjutsu, which would be the manifestation of Chakra. This was also not technically Ninjutsu, as he never intended to use Chakra as a weapon.
The Ninjutsu as we know today is a corrupted version of Ninshu, something that the Sage of Six paths spread around. He understood that with Chakra, people could connect to each other. However, his son, Indra Otsutsuki, after being corrupted by the Black Zetsu, invented Ninjutsu, which would be used to gain power by brutal force. Hagoromo did not approve of these means.
Following this, over the years, Humans used Ninjutsu in order to wage wars and fight each other, in ways Hagoromo, the Sage of Six Paths never intended to go. In the era of peace, Ninjutsu is still used by Shinobi, to a point where even Scientific Ninja tools are developed.
There are many Ninjutsu that are seen in the Naruto Universe. Some have Natures added to them, while the others are raw manifestations of Chakra. Here are some examples of Ninjutsu that are seen in the anime:
Rasengan is one of the hardest Ninjutsu to master as this is an example of a Ninjutsu which requires extreme chakra control. The user manifests Chakra in their palm and changes its form to make it into a fast, spiralling ball which deals incredible amounts of damage.
This version of the Rasengan adds the Wind Nature into the Rasengan and is an example of incorporating Nature to a Ninjutsu. By adding the Wind Element, the Rasengan is much stronger than normal.
An example of a Ninjutsu is the manifestation of Chakra within the body. After casting enough hand signs to mould chakra within your body, the caster releases it in order to form Shadow Clones, which are solid clones of the user.
Fire Style: Fireball Jutsu is a type of Ninjutsu that is inherently infused with an element. In order to perform this Jutsu, one must cast hand signs and mould Chakra inside them and then shoot it out as a ball of fire.
Kamui is a part of the visual prowess called the Mangekyou Sharingan belonging to Obito Uchiha. This visual prowess utilises space-time Ninjutsu. It allows the caster to transport something from one place to another.
Naruto masters the Rasengan in just one week, winning his bet against Tsunade and defeating Kabuto in a battle of survival.
Naruto finally adds the Wind Nature into the Rasengan and reaches the battlefield just in time to save his team. Naruto uses the Rasenshuriken for the first time.
Naruto creates a thousand Shadow Clones in order to defeat Mizuki. He defends Iruka from Mizuki, despite him being a Genin.
Kakashi is surprised to see Sasuke casting the Fireball Jutsu, since it requires too much chakra. Sasuke still manages to cast a perfect Fireball.
Kakashi uses the Space-time Ninjutsu, Kamui in order to remove the projectiles which were being targeted at Choji and himself. Although he dies in the process, he still manages to obtain essential information to save the leaf.
A. Rock Lee can not use Ninjutsu because he does not have Chakra flowing in his body. While he can learn Shuriken Jutsu, he still prefers Taijutsu over that so he honed his Taijutsu skills.
A. Although Ninjutsu existed before the creation of it, the actual creation of Ninjutsu as we know today was done by the Sage of Six Path’s son, Indra Otsutsuki.
A. Although it isn’t advised, Ninjutsu can be used continuously, even as a barrage. As long as the user has Chakra, Ninjutsu can be used. This is not advisable because conserving Chakra for later is an important part of being a Shinobi as extinguishing Chakra can lead to death.