Naruto: The five hardest ninjutsu to learn

1. Rasengan: A powerful ninjutsu created by Minato Namikaze, the Fourth Hokage. Only those closely connected to him, like Naruto and Boruto, can use it. 

2. Eight Inner Gates: A physical technique that surpasses regular ninjutsu. Opening the eighth gate, the Gate of Death, is extremely rare. Naruto's powers saved Rock Lee. Mastering the Eight Inner Gates requires dedication and perseverance.

3. Susano'o: A difficult technique that requires unlocking the Mangekyou Sharingan. Only absolute geniuses possess this ability, except for rare cases like Kakashi. It doesn't reflect their true strength.

4. Sage Mode: Establishing a good relationship with one of the three Great Sages is necessary to achieve Sage Mode. Jiraiya combined it with the power of two sages. Naruto, Orochimaru, and Tsunade couldn't learn it.

5. Six Paths Power: This technique requires someone to teach it. Only descendants of the Six Paths Sage can learn it. Naruto's Six Paths Power has incredible abilities, including resurrecting the dead. It is a unique and powerful skill.