Kurai senko

jai uchiha first created this jutsu when jiraiya told him and naruto that they needed to try and advance the power of their most powerful jutsu, jai chose rasengan but decided to use chidori to bump up the power level, he managed to create a black ball with a powerful spin and a negative electrical charge, the jutsu was so powerful that jiraiya told jai not to teach anyone how to use it.

the jutsu looks like a black version of the rasengan with white sparks flying off it, and its destructive power is double that of the rasengan and capable of destroying an entire building.