When they get together, Kendrick Lamar and BJ the Chicago Kid are two complementary forces, taking the template of hip-hop and using it to create something more akin to bluesy, agitprop emo that just happens to feature some rapping. The only obvious precedent for this type of stuff is when Jay-Z showed up in the bonus tracks of Raphael Saadiq's The Way I See It, or maybe a super tasteful version of what Everlast did in his Whitey Ford period?
Stream: BJ the Chicago Kid f. Kendrick Lamar, "The World Is A Ghetto"