Watch Fist of the Blue Sky: Regenesis 2nd Season Online

Following a cataclysmic nuclear war, the world teeters on the brink of complete destruction. Civilization is polarized into a degenerate society where opposing packs of marauding scavengers prey on helpless, homeless nomads. For those who are lucky enough to survive the constant brutality and danger, it is a bleak existence. Life an death blur into abstractions. The only hope left for mankind is to find a hero worthy of becoming the next "Fist of the North Star" - an enlightened warrior - who is capable of leading those with the will to survive out of this barrenness into a new world. But in this savage no-man's land of shifting loyalties and power-hungry demi-gods, heroes are in short supply. (Source: AniDB)

The fourth part of the new Hokuto no Ken pentalogy (3 movies, 2 OVAs).

Kenshiro is the heir of the legendary martial arts known as Hokuto Shinken, which can kill a man with a single blow, by striking the pressure points in the enemy's body. Hokuto Shinken can be passed only to one successor at a time. When he was chosen as the successor, he parted ways with his brothers, Toki and Raoh. The former decided to use what he knew of the art to cure people... while the latter has chosen to use his supreme strength to install peace in the world by power. Kenshiro is accompanied by Lynn and Bart, and the movie's story begins when an overlord starts kidnapping children to use them as slaves for building his own pyramid... (Source: AniDB)

Last of the Shin Kyuuseishu Densetsu pentalogy. A prequel set between Kenshiro's defeat at the hands of Shin and the beginning of the manga.

In the year 19XX, after being betrayed and left for dead, bravehearted warrior Kenshirou wanders a post-apocalyptic wasteland on a quest to track down his rival, Shin, who has kidnapped his beloved fiancée Yuria. During his journey, Kenshirou makes use of his deadly fighting form, Hokuto Shinken, to defend the helpless from bloodthirsty ravagers. It isn't long before his exploits begin to attract the attention of greater enemies, like warlords and rival martial artists, and Keshirou finds himself involved with more than he originally bargained for. Faced with ever-increasing odds, the successor of Hokuto Shinken is forced to put his skills to the test in an effort to take back what he cares for most. And as these new challenges present themselves and the battle against injustice intensifies, namely his conflict with Shin and the rest of the Nanto Seiken school of martial arts, Kenshirou is gradually transformed into the savior of an irradiated and violent world. [Written by MAL Rewrite]