Killer B is one of the most iconic characters in Naruto. After all, other than the fact that he is a Jinchuriki just like Naruto, his devil-may-care attitude amidst every tough situation is such a breath of fresh air to the increasingly heavy story in the latter part of the series.
That being said, just like everybody else, Killer B has gone through a lot during the time period around the Fourth Great Ninja War. So how has Killer B changed throughout the series? Is there anything that changed with this rapping Shinobi in the first place?
The First Time Killer B Appear in the Series
The first time we truly get to see Killer B is when Sasuke and his team Taka infiltrate Kumogakure. Taka is part of Akatsuki at the time, and their first official assignment is to kidnap the eight-tailed Jinchuriki, which is Killer B. Sasuke, Suigetsu, Karin, and Jugo work together to attack Killer B, but the man himself seems quite relaxed and easily overpowers them all. B even has the time to write some rap verses in his rhyme book while fighting against Sasuke at the same time.
At first, Killer B uses his iconic seven-swords technique, but once he gets serious and enters the Bijuu mode, Killer B single-handedly annihilate Sasuke and Taka. In fact, if Jugo and Karin were not there, Sasuke would have already died. Sasuke needs to use his newly-acquired Amaterasu in order to incapacitate Killer B. Even then, he actually uses one of the eight-tailed tentacles as a clone of himself, while the real Killer B takes this chance to wander off into the outside world, away from the prying eyes of the village.
Killer B in the Past
B was an orphan boy living by himself in Kumogakure. At the time, the village was looking for the new Junchiriki for the eight-tailed beast. In order to test the ability of the prospective candidates, the village decided to hold some sort of exam. Killer B passed the test with flying colors and was not only appointed as the new Jinchuriki, but also as an adoptive brother to Kumogakure's future Raikage, a strong yet loving man named A. Both of them became the A B combo and often took on dangerous missions together.
Just like any other Jinchuriki, little Killer B has to face hatred and prejudice from the people in the village every single day. But his natural carefree and positive attitude along with the full support of his brother enabled B to simply shrug it off and focus on creating dope rhymes instead. In time, Killer B became the only person in the history of Kumogakure who was not only able to tame the eight-tailed beast but also became friends with it. And as he helps save the village multiple times throughout the years, Killer B finally becomes a beloved figure in Kumogakure.
Killer B After He Met Naruto
Killer B is asked by his brother, the Raikage, to help Naruto master his Bijuu power. Not only that, his other mission is to hide Naruto from Akatsuki. Because other than the eight and the nine-tailed, every other Bijuu has been captured and extracted out of their respective Jinchuriki. In a way, Killer B is not only acting as a mentor to Naruto, but also as his protector. Throughout the series, Killer B has always been a carefree, stubborn and free-spirited person, sort of like Naruto. That's why it doesn't take a long time for both of them to be fast friends. But what Naruto has over Killer B is his strong conviction to help everybody in his village. After all, Naruto wants to be a Hokage, so such determination is a must.
On the other hand, Killer B never wanted to be a Raikage. He has the utmost respect for his brother, and he also cares deeply about the well-being of his comrades, but being a leader is the furthest thing on his mind. That is why Killer B doesn't have the same drive to get better and stronger for the sake of the village like Naruto. However, meeting and spending time with Naruto slowly changes how Killer B sees everything around him. For the longest time, he only does things according to what his brother told him to do and only uses his free time to have fun and make some rhymes. But he begins to see the bigger picture now. He still doesn't have any interest in being a Raikage, but he now understands the conviction and determination of someone who strives to get that title. That is why he chose to put his trust in Naruto, even if it meant going against his brother's will.
After the events of the last arc, Killer B and Naruto are the only remaining Jinchuriki in the world. He lives with the eight-tailed for so long that they are practically like a best friend now. He may be the same mischievous rapping shinobi as he used to be, but now he has become somebody who bears a similar conviction and determination to protect his village just like a Raikage, while still staying far away from all the boring work and responsibility that comes with the title.