In particular, they wanted Dik to eliminate Hui Mun Keung both in revenge for Kyoko Yamaguchi and also to remove a huge obstacle in bringing Shanghai under Japanese control. As long as Hui Mun Keung remained the most powerful man in Shanghai, that would be a tough goal to accomplish, so Dik was sent in to murder Hui Mun Keung.
BTW, what are your thoughts on Chow Yun Fat's brief cameo as Hui Mun Keung (in flashback) from Episode 4 of BUND II?
I thought it was really neat; that scene more or less made the sequel for me.
His later transformation into a sophisticated gentleman (similar to Hui Mun Keung) was a bit sudden. Not that he couldn't have made this transformation, but it should have been a more gradual process.