"Iruka's Ordeal" (イルカの試練, Iruka no Shiren) is episode 177 of the Naruto: Shippūden anime.
After being denied a chance to join his classmates on a "Test of Courage", Naruto decides to pull a prank on them. Whilst browsing a selection of masks at a shop, he is forcefully pushed out the store by the shopkeeper, who proceeds to hurl a mask at Naruto's head, telling the boy to stay out. Hurt, Naruto picks up the mask, and runs away as he notices everyone on the street staring at him. Unbeknownst to him, Shikamaru and Chōji are also present, with the former wondering why Naruto is treated so badly.
Naruto heads to the Konoha Cemetery wearing his mask and tricks Hibachi, one of his bullies. Iruka witnesses the frightened kids running and approaches the masked Naruto with a kunai. As Naruto takes his mask off, Iruka sheathes his kunai and recalls how he felt when his parents were killed by the Nine-Tailed Fox that is now sealed inside Naruto. Seeing the look on his sensei's face, Naruto asks how come everyone looks at him in that manner and runs away, vowing never to return to the Academy.
The following day, Iruka runs into Kakashi, who notices that his eyes are now lifeless. In the past, Kakashi was the squad leader on a mission Iruka was sent on, and the mission was endangered by Iruka's compassionate nature towards enemy shinobi. Deciding to use his compassion for good, Iruka asked the Third Hokage to have him appointed as an Academy instructor so that he could pass on the Will of Fire to the next generation. Kakashi remarks how Iruka's eyes held a spark that day, but that they are now dull. Iruka tells Kakashi that he cannot tolerate Naruto, albeit knowing that it is not Naruto's fault for housing a demon within him and that Naruto is just too troublesome to handle. However, Kakashi tells him that he is the only one who can touch Naruto's heart and adds that it would be Iruka's personal ordeal to do so. Later that evening, Iruka spots Naruto playing with kids on a playground. As the kids' parents come, a mother reprimands her child for playing with "that kid", something Iruka and Shikamaru both notice. As the kids and parents leave, Naruto grows sad at the fact that he has no parents to go home to and that the other parents do not like their kids playing with him. Later that night, Shikamaru asks his parents why people treat Naruto like the plague. Unable to tell Naruto the truth, Shikaku merely tells his son to ignore how the others treat Naruto and to treat Naruto in whatever way he wishes to treat him.
The next day, Hibachi tricks Naruto into heading to the back hills where enemy corpses are laid, promising to be his friend if he does so. Naruto, ecstatic at the prospect of finally having friends, rushes to the hills. In class, Iruka notices that Naruto is still absent and asks Hibachi if he had seen him, to which Hibachi lies and claims that he did not. Shikamaru, who had overheard Hibachi tricking Naruto, exposes Hibachi's prank to the class, and Iruka rushes out to intercept Naruto.