5 years after the annihilation, Kai killed Raikitchi and after that he suddenly passed out and when he woke up he was with a masked man whom told him about his top secret mission. After knowing the truth he went ahead and decided to kill Kaidara for what he did in forcing Raikitchi and the masked man to kill the Uchihas.
Kaidara: Kai what are you doing here at this late ?
Kai: ...
Kaidara: Kai answer me!
Kai: I have a question first.
Kaidara: If you have then tell me
Kai: Who the hell are you to force Raikitchi to kill the Uchihas and lie to me all this time!!!
Kaidara: So you've found out about the truth.
Kai: And now your going to pay!
Kaidara: I did it only for peace.
Kai: No you didn't ! You were just afraid to lose your position because majority of the Uchihas are on Raidara's side! Is that a valid reason to force others to dishonor themselves by killing their own flesh and blood!
Kaidara: Fine then... kill me (If Johnny finds out about this then the brother's battle cycle would be balanced)
Kai: Die!!!!!!!!!!!!!!!!!!!!
Kai: Good Riddance.
Johnny: What did you do to Kaidara?
Kai: I killed him to avenge our clan!
Johnny: He didn't kill the clan. Raikitchi and Johnathan did it!
Kai: No! They were forced to kill the Uchihas by Kaidara!!!!
Johnny: I don't believe it!
Kai: Then believe your liar shogun.
Johnny: He is not a liar so shut up and die!!!
Kai: So you've inherited Susano'o's abilities
Johnny: Definitely
Kai: Johnny!!!!!!!!!!!!!!!!!
Johnny: Kai!!!!!!!!!!!!!!!!!!!!!!
So both friends died trying to avenge someone. Kai died because he fall into an abyss after falling from the sky because of the explosion of powers during his battle with Johnny while Johnny fell into a volcano.