"Kakashi Chronicles ~ Boys' Life on the Battlefield ~ Part 1" (カカシ外伝～戦場のボーイズライフ～前編, Kakashi Gaiden ~ Senjō no Bōizuraifu ~ Zenpen) is episode 119 of the Naruto: Shippūden anime.
Obito Uchiha rushes to a clearing where his teammate Kakashi Hatake admonishes him for being late, declaring that the shinobi rules of conduct state that a shinobi is to be on time. The team's leader, Minato Namikaze, tells them they have a new mission, and that since Kakashi has just become a jōnin, he would be leading himself, Obito and their other teammate Rin Nohara while he goes on his own mission. In order to celebrate Kakashi's promotion, Minato gives Kakashi a Flying Thunder God Kunai while Rin gives him a specially made medic-kit. Obito, however, has forgotten to bring a gift for Kakashi and is vexed when Kakashi states that it would have been useless anyways.
Minato tells them that as they are involved in a war, Iwagakure has invaded Kusagakure near the Land of Fire and that Kakashi's team are to destroy the Kannabi Bridge in order to cripple their efforts. Meanwhile, he would engage in combat in the front lines in order to provide a suitable distraction. On their way, Kakashi spots Mahiru, an Iwa-nin who is conducting surveillance. Minato notices that Mahiru has employed about twenty shadow clones while Kakashi tells him that he has a new technique that should be able to deal with them all. With his Chidori, Kakashi plows through the shadow clones and rushes towards the real Mahiru; however, Kakashi's Chidori causes him to have tunnel vision and thus does not see Mahiru pull out a sword. Before Mahiru can kill Kakashi, Minato manages to save him from the blow whilst simultaneously marking Mahiru's foot, although Kakashi ends up being slashed near his underarm.
As Rin tends to Kakashi's wounds, Minato uses his Flying Thunder God Technique to appear before Mahiru, placing a kunai next to the Iwa-nin's throat. Mahiru expresses his regret for recognising Minato as the famed "Konoha's Yellow Flash" and for not retreating as per Iwagakure's rules; Minato then kills Mahiru. As they camp that night, Obito expresses his displeasure of being a failure from the elite Uchiha Clan while having to deal with Kakashi's genius. Minato reveals that Kakashi is the way he is because his father Sakumo, who was known as the "Konoha's White Fang", had once broken the law by choosing to save the lives of his comrades over completing the mission and was thus vilified by both the village and the very friends he had saved. Unable to cope, Sakumo took his own life. Since then, Kakashi had chosen never to speak of his father and vowed to upheld the rules and regulations of the shinobi world.
The following morning, Minato sets off on his own mission while Obito decides to pledge his loyalty to his new captain, Kakashi, much to the team's surprise. On their way to the bridge, they are spotted by twoenemies from Iwa. While one of them distracts Kakashi and Obito, the other uses a camouflage technique to abduct Rin. Obito claims that they should go and save Rin, only for Kakashi to remind him that the law is to complete the mission even at the expense of their comrades, and that they should not let emotions cloud their judgment. Obito declares that he will not follow Kakashi's orders, and as he walks away, he tells Kakashi that he personally views the White Fang as a hero; he also adds that while shinobi who break the rules are considered scum, those who abandon their friends are worse than scum. The duo then part their separate ways.