The original movie was based on the popular manga by Wakui Ken and features Ayano in the leading role of Shiratori Tatsuhiko who was initially penniless but rose up the ranks of the underworld in Shinjuku's Kabukicho. In the new movie, the company which he works for will make inroads into Yokohama which leads to a battle between the rival gangs from there and Shinjuku. Hirose will play the role of a hostess named Mayumi while Asano will play the most feared boss in Yokohama named Taki. Shiina Kippei will play a key figure who makes the rivalry between Shinjuku and Yokohama even worse.
The movie's producer Yamamoto Mataichiro revealed that when they were making the first movie, they were already thinking of doing Part 2 since all the characters were alive and kicking. However, he suffered from a slipped disk between January and March last year so he was trying to write the script at the same time as the filming for Part 2 was going on. In the end, they ended up with a 3 hour 40 minute film which had to be condensed to 2 hours so it felt like a rollercoaster ride to him.
Sources: Sanspo 1 / Sanspo 2