Rule #1 of the movie business - If it works, beat it to death. "The Street Fighter" worked so he returned. Back in the 1970s movies with violence could get an "X" rating. If your copy is only about 75 minutes long then you have the censored version. I have read the complete version is 83 minutes but I have also read 90 minutes. The second rule of movies is when making a sequel just do the same stuff over again but this time a bit longer and harder. This movie followed both rules resulting in viewer enjoyment and producer profit. I rate it just a tad above average for the year and genre based on that. I considered deducting a point for the annoying side kick but at least she's cute.
The movie opens with Sonny offered big money to get two guys. He negotiates for double the money. The first guy is in police custody so Sonny gets arrested. He cuts the guy's throat then escapes by defenestration. (The first movie had two defenestrations.) He discusses his second target with his new sidekick, a girl.
What style of martial arts did Sonny Chiba show in his movies? He practiced kyokushin, ninjiutsu, goju-ryo, shorinji kemo, judo, and kendo. Before he started martial arts, Sonny did track and field, baseball, and volleyball in high school. To take this to the next level, on the advice of a coach, he dedicated himself in artistic gymnastics. In his movies his moves seem more reflective of that rather than any martial arts style.