Taking place in 1930s Japan and China, Kasumi Kenshiro(the uncle of the lead from Fist of the North Star) is forced to leave his teaching job and settle an old gang rivalry with the help of his martial arts. Along the way, he meets the son of one his triad buddies, an old flame, and a mysterious old man who teaches him new techniques which will assist him in his quest.

From Anime Network

Mysterious assassin Mayo, a Japanese man in Malaysia, will kill anyone you want for just five dollars. Of course, he'll kill you for five dollars too, but doesn't that just even the score? With outcast allies at his side and formidable enemies against him, Mayo is the only one who can stop a conspiracy that stretches around the world!

Toki is a former Hokuto practitioner, and his incredible strength coped with his knowledge of the assassin art would be enough to call him devil.... But Toki's kindness and desire to help people prevent them from calling him devil, they instead can only whisper words akin to that of 'savior'.

Follow the friendship of Tetsu and Gorou from the Koushien to adulthood.

The gag manga centers on a fun version of the Holy Emperor Souther as he tries to find ways to become friends with Kenshirō, demonstrates his party techniques, and sometimes plays with the Gosha Sei.

A deeper look at the childhood and history of Jagi, one of the four Hokuto brothers, and an important villain in the original Hokuto no Ken manga.

Heat is a crime story featuring a young man named Tatsumi Karasawa who suddenly rises in the criminal world of Shinjuku, Tokyo, and becomes the leader of a group of amateurs who show no reluctance to face police and gangs alike. His successes in the Tokyo underground make a chief and a yakuza boss plot a conspiracy to eliminate him.

199X, nuclear war has ravaged the planet. From the ashes, gangs have risen to take all the power from world governments. Justice has ceased to exist in this now lawless world. From the ashes of a desert a man appears. His name is Kenshiro, and he is the sucessor to the most powerful martial art in the world, Hokuto Shinken.

This art attacks the foes insides, and makes him explode internally, dying in often brutal ways. Kenshiro's goal is to kill the man who kidnapped his fiance, Yuria. A man that he once called friend, but whom betrayed him and left him for dead. Along the way he makes friends and enemies alike, while protecting those who cannot protect themselves.

The story is loosely based on the Three Kingdoms period, using both real and original characters and events from the historical period in Chinese history and folklore of the Romance of the Three Kingdoms.
(Source: MU)