Nagai Jinsei, aka "Bare-Knuckles Jinsei". Born in a dumpster, raised in an orphanage, living as a yakuza, he is tough enough that he fights all his fights bare-handed, and is covered with countless knife and bullet scars from his battles. But his life changes when he saves the five-year-old Ayumi, daughter of the new police chief, Enjoji Masayoshi, and befriends their family. For the first time in his life, Jinsei feels like he's found a family of his own, and decides to start his life over, but his past and his ties to the yakuza keep getting in the way.

(Source: MangaUpdates)

This is a no holds barred story about an ex biker gang leader turned Cop, Kenji Date.
Operating under the nickname of 'Hyena', Date rubs pretty much everybody within the police force the wrong way as goes about his business ridding the city of all it's scum.

When an American scientist carrying a cure for the AIDS virus is kidnapped by an arms merchant, John Kyosuke is forced back from retirement. He accepts the challenge to regain posession of the anti-serum. He finds out that some of the people he is after are closely related, which gives his conquest a whole new meaning...

(Source: MU)

28 years earlier, there was a plane crash in the mountains of Gifu Prefecture. The barrier that the Kobo Daishi, Kukai had created to seal away the demons was destroyed in crimson flames... Present day, Oniwakamaru, King of the Yokai, appears inside the body of pure and innocent Tachibana Hitori!!

M60-toting Kenji Hado, known as "the Hard", pays his divorce bills by working in the US as a bounty hunter. Masseria, a ruthless and ambitious mafia boss, targets his family - starting with the Hard's father-in-law, a Don in the NY mafia. Hard's aim, while poor when sober, becomes extremely accurate when drunk! The short story N.Y. Dust, in volume 12 of Riki-Oh, was the prototype for The Hard.
An anime was made of this series.

Art equals expression, an expression creating an outer form, expressing joy, sorrow, and the darkness of the soul. Yutou Riro is a student at an art college, but she believes she lacks the talent to truly succeed as an artist. Entering her life through a series of coincidences is Karaba Jou. To Riro's astonishment, Jou has an exceptional ability to draw the "real" self of the people/object he draws. His artwork draws attention to the finest details of his subject, bringing to light the truth behind each individual.

(Source: MangaHelpers)

The story is set in a dystopian near future where the Japan society is experiencing a crime rampage and in which a powerful and secret religious organization, with mysterious goals, is acting as an invisible hand behind the scenes.
The main character is their strongest assassin, lended to them by his fanatic mother when he was a child, and now became a ruthless killing machine whose fists and feet cause serious damage to his adversaries, and whose weapon of choice is a special cutting wire with which grabs and scorch the opponents.

He's a man hunter, whose childhood has been stolen and molded after his tormentors, but when the road of forgiveness is precluded to him what can be left to a man to obtain the redemption?
Takeo finds the answer in the vengeance, and in eradicating that same evil from which he has born.

So this dark and impressive badass guy, after betraying the sept, gets down to business kicking their ass and unleashing his fury against the deadly opponents sent to stop his unparalleled revenge.

This is a continuation of Koko Tekken-den Tough which ran for 42 volumes and followed the main character, Kiichi, when he was younger and was training under his father Seiko Miyazawa. This is a mixed martial arts fighter manga about the Miyazawa school of martial arts. Initially, it is about Kiichi trying to heal his father after he was nearly killed by his brother Kiryu but it then goes on to be less about that as his father recovers and some tournament style fighting begins.

From Viz:
Nobody enjoys a good fight more than "Kiibo" Miyazawa, a high school student whose father is training him in the family's secret martial art. Kiibo dreams of becoming the next Bruce Lee, but his awesome fighting skills may soon surpass his idol's!