Total Recommendations: 2
-Both deal with immortality(with both MC's being one) -Both have obstacles regarding the consequences of immortality attacking mortals -Both have the MC's travel to a new location and explore new people/towns Ningyo is a lot more episodic in nature while Fumetsu builds up from last adventure. Unfortunately, Ningyo was cut short due to other projects (so no proper end) ,while Fumetsu is a long-running manga (which may have a proper conclusion in the future).
While Banana Fish (BF) focuses more on mafia while Hai to Diamond(HtD) on prostitution, both have a very similar premise: -black haired Japanese boy entering a world of gangs and sex -feature a light-haired american (whose name consists of 3 letters) who is familiar with the harsh world -american has a history of prostitution and learned how to pick up a gun -american slept with mafia boss through force, which introduced them to the harsh world -involve an older brother becoming unstable (and "dead" in a way) due to some involvement from mafia -involve chinese mafia (though one of mangas it's only temporarily) -and prolly more, but this is more than enough However, HtD corrupts the Japanese boy(BF doesn't) and the series in general is more geared towards Yaoi (w/ both MC's together),whereas BF focuses on politics&drugs w/ a maybe-not-even BL tone. In my opinion, BF gives a lot more of a satisfying characterization & storytelling, but a smaller cast in HtD gave way for more steady & rounded storyline. Regardless, both are still great reads.