Kowloon has some serious gritty charm. I was in Hong Kong some years ago for a friend's wedding and Hong Kong Island is fairly modern. Across the bay, after a ferry ride and walking away from the waterfront, stepping into the heart of Kowloon (urban area/peninsula) felt like walking into a bustling, neon-lighted, jumbo modern Chinatown (but not some touristy historical district; skyscrapers, giant vertical malls, row upon rows of small shops and street vendors, and the food... holy moly) that all other Chinatowns aspire to be. Certain districts of Shanghai also had this feeling.
As noted in the manga, Kowloon Walled City (within Kowloon City district on the Kowloon Peninsula) was demolished in 1994. The land has since been turned into a park, surprising given the value of land in HK. While the park is nice, it feels... out of place? Boring? If the Walled City was still around, given the crime and gangs that used to run the place, I suppose I wouldn't have actually visited it but I'm sure it'd be particularly gritty?
Edit: Clarified Kowloon Peninsula vs. Kowloon Walled City (referred to as "Kowloon" in this manga)
Anyways, this manga makes me want to visit Hong Kong again.
Oh, and yes, the mystery deepens!