Kakashi Hatake, more commonly known as the Copy Ninja of the Hidden Leaf Village, was one of the strongest shinobi in Naruto. Not only was he the teacher of, arguably, the strongest team of genins, Team 7, but he also had a past in Anbu Black Ops and became a jonin when most students qualified to become a genin.
The Copy Ninja enjoyed a healthy rivalry with the taijutsu master of the Hidden Leaf Village, Might Guy. They even considered themselves eternal rivals and never left a chance to compete against one another. Before the Fourth Great Ninja War, he stood 51-50 against Guy.
However, things changed during the war, as after Guy's Eight Gate of Death transformation, the copy ninja admitted the former had surpassed him. Nonetheless, during the end of the war, the copy ninja achieved Perfect Susanoo. Yet, even with such a strong technique up his sleeve, he couldn't have stood a chance against the Eight Gate Guy.
Naruto: Why Kakashi would lose against Guy even with a perfect Susanoo
Kakashi Hatake was the teacher of Team 7 and a former member of Hidden Leaf's Anbu Black Ops. Since childhood, he was a talented boy and achieved the title of a jounin when he was in a team of genins taught by Minato Namikaze.
Misfortune befell his first mission as the leader of his team, which resulted in the death of one of his teammates, Obito Uchiha. Before he was crushed under the rumble, he passed one of his Sharingan, the prized kekkai genkai of the Uchiha clan, to Kakashi and requested him to protect Rin.
Unsurprisingly, Kakashi got used to the Sharingan in no time and was declared the Copy Ninja soon enough. This is because he used the visual prowess of the Sharingan to observe the movements of others and copy their techniques, no matter how hard they were.
During the first mission of Team 7, the Copy Ninja copied Zabuza Momochi's jutsu in front of his eyes, matching his speed of weaving hand signs. Later, he was also able to copy the Rasengen, the priced jutsu of the Fourth Hokage, and many more, such that he was known as the Shinobi who had copied over 1000 jutsu techniques.
The copy ninja considered the oddball, Might Guy, an eternal rival of his. Might Guy was a person who couldn't use any ninjutsu and had to rely on his taijutsu in combat. Their rivalry reached a point where the copy ninja surpassed him (51-50), but nothing was decided as their rivalry didn't end.
During the last part of the Fourth Great Ninja War of Naruto, Guy had to sacrifice himself to save the next generation of Shinobi. So, he unlocked the Eight Gate of Death of his Eight Inner Great Formation and pulverized Madara Uchiha who escaped death by a hair's breadth. After this fight, the copy ninja declared Guy superior to him, and for good reason, because the latter was able to suppress a God.
At the climax of the Fourth Great Ninja War of Naruto, Obito died and passed both of his Sharingan eyes to the copy ninja. This made him capable of activating the Susanoo, which required a Mangekyo Sharingan, which both of them had already awakened at Rin's death. The copy ninja activated his colossal technique and was a key part of saving the world alongside Team 7.
Even though he had declared Guy superior to him, could his Susanoo have made a difference against Guy? As mentioned earlier, Guy was almost able to take down a God, Madara Six Paths, with his Eight Gate of Death, so, the copy ninja's Susanoo couldn't have been any better.
In the starting phase of the Fourth Great Ninja War, Tsunade tried to attack Madara's base Susanoo but was hardly able to put a crack in it. On the other hand, Guy managed to almost kill the same Madara but in a much stronger form, the Six Paths. So, even at his peak, Kakashi couldn't have been a match for his eternal rival, Might Guy.
Read Also:
Naruto: Why is the copy ninja so famous and well-known?
Naruto: How old was the copy ninja when Minato died? Explained
Naruto: Why did the copy ninja never get married in the series? Explained
Naruto theory explains how the copy ninja can get his Sharingan back
Naruto: Why did Sasuke never address the copy ninja as sensei? Explained