http://www.mangago.me/read-manga/heart_strings/
http://www.mangago.me/read-manga/beast_feast/
http://www.mangago.me/read-manga/sugar_code/
http://www.mangago.me/read-manga/honto_yajuu/
http://www.mangago.me/read-manga/gokudou_darling/
http://www.mangago.me/read-manga/koi_made_hyakurin/
http://www.mangago.me/read-manga/trigger/
http://www.mangago.me/read-manga/houkago_no_love_call/
http://www.mangago.me/read-manga/bi_no_isu/
http://www.mangago.me/read-manga/totally_captivated/
http://www.mangago.me/read-manga/tight_rope/
http://www.mangago.me/read-manga/kyou_hana_no_gotoshi/
http://www.mangago.me/read-manga/aiso_tsukashi/
http://www.mangago.me/read-manga/namaiki_na_ryouken_no_shitsukekata/
http://www.mangago.me/read-manga/ake_nure_goyou_ni_furu_yuki_wa/
http://www.mangago.me/read-manga/usagi_otoko_tora_otoko/
http://www.mangago.me/read-manga/ikoku_irokoi_romantan/
Gangster/Mafia/Prison/Yakuza yaois:
Anohito To Nitenai Kuchibiru (the last chapter)
1999nen 7 no tsuki Shanghai
Acid Town
Ai ga Kami wo Korosu Toki
Aibu
Affair
Afuresouna Pool
Aiso Tsukashi
Ake nure goyou ni furu yuki ha
Beast & Feast
Bi no isu
Blind Love
Boku no Shiru Anata no Hanashi
Border
Buddy System
Datte Ai ja Nai!?
Deadlock
Don’t stay Gold
Finder (Series)
From Dusk Till Dawn
Fukuin
God of Dogs
Hana to Ryuu
Harem Days
Heart Strings
Honto Yajuu
Ikoku Irokoi Romantan
Illumination
Junai ni torawarete
Kizoku no Aoi Seppun
Kizuna
Kyou hana no gotoshi
Like as the time will come when it will rain
Love or Pride
Love Mode
Lucky Dog 1 blast
Missing Code
Morotomo
Negai kanae tamae
NightS
Noodle Shop Affair
Okane Ga Nai
Otoko Hiroimashita
Night Walk
Running on Empty
S
Saezuru Toi Wa Habatakanai
Seishun no yamai wa
Shibuya de aimashou
Shisei no Otoko
Shounen wa Ashita wo korosu
Sleeping with Money
Sugar Code
Taka ga Koi Daro
Tengoku e ikebaii
Tenshi no kokoro de
The Summit
Tight Rope
Tokyo Yabanjin
Totally Captivated
Totally Spying on them
Trigger
Tsumasaki ni Kiss
Uchi no tantei shirimasenka?
Under Grand Hotel
Under Grand Hotel - Kiss & Kill
Usagi Otoko Tora Otoko
Uso to Coffee to amai kiss
Wild Adapter
Yajuu Shugi
Yakuza in Love
Yuigonjou Yori Ai wo Komete
Yorube Naki Mono
You're my loveprize in viewfinder
Hi! Any yaoi manga that has yakuza/mafia? That's not viewfinder cause I read that already and it's awesome as hell and now I want more. Please and thanks! :D