It's natural for any big-name title to get spin-offs. Saint Seiya had it's movies and live-action musicals, Dragon Ball has a ton of movies, OVAs, and even spin-off mangas, and even Ring ni Kakero apparently got a reality show where potential boxers can enter to make it big, just to name a few. Hokuto no Ken/Fist of the North Star is certainly no exception, as it's had a bunch of spin-off mangas (all of the "Gaiden" manga based on the major characters, with the most-well-known being Raoh Gaiden/Legends of the Dark King), OVAs/movies (the New Savior Legend series of films), etc. But there's also a smaller name spin-off to FotNS that some fans might write off simply due to the use of super deformed character designs. That title is DD Hokuto no Ken.
DD Hokuto no Ken, which doesn't exactly translate as easily as it should (the "no" in this title is not the hiragana の but rather the kanji 之, which is an antiquated usage & done as a pun), is a gag manga that takes the characters of FotNS and puts them in a 199X world that isn't destroyed by nuclear apocalypse. Therefore, the Hokuto brothers live normal lives (Raoh works in construction, Kenshiro works in an office [Hokuto Hundred Crack Fist does wonders for his typing skills!], and Toki is jobless due to illness; Jagi is still a crook, though), but the big part of the comedy is that all of these characters still maintain the character traits they have in the original series. The manga runs in Monthly Comic Zenon, which is the replacement magazine for Comic Bunch after it shut down, and at the beginning of this year a 12-episode anime adaptation aired on television. Comprised of 3-minute episodes, 3:30 if you count the opening sequence, this show takes no time in getting straight to the jokes and purposefully-awkward situations and can easily be watched fully in one go. But is it good?
DD's greatest positive is that it's able to utilize just about every major character in some fashion and make them all highly entertaining to watch; seeing how DD fits each of them into a "normal" world is really cool. Shin is the head of a host club, Yuda runs a salon, Souther is the president of the Holy Emperor Construction company, Rei is a supermodel, Shu is a detective, legendary seiyuu Shigeru Chiba himself (who is well-loved as the crazed narrator of FotNS) is in the show as a muscular news reporter called Muscle Chiba, etc. In fact, the only odd absences are from Mamiya and Rei's sister Airi, who make absolutely no appearances in the show whatsoever, not even in a cameo, as well as some semi-major villains like Zeed or Boss Fang, but they are at least referenced to. You can also say that the characters from the FotNS 2 TV series are missing, but considering how modern canon of the series ignores everything that happened in that show aside from the country of Ashura existing, which is referenced in one DD episode, it's not surprising to see the likes of Ein, Falco, Jakou, and Kaioh missing. You definitely have to have seen at least the original 109-episode FotNS TV series, or the manga equivalent, in order to fully this series, though, as many of the jokes made here are in reference to moments from the series as well as the previously-mentioned jokes coming off of each character's maintained character traits clashing with modern society. For example, Raoh still has his mind on conquest, even if it's as simple as Soba noodle conquest, and there are a good amount of famous lines that are altered for comedic purposes (just count how many times Kenshiro alters his famous "You're already dead"). If you're a newcomer to this series then I say avoid DD, as it can actually spoil some parts of the story.
In stark contrast to Tetsuro Hara's uber-manly art style, DD's character design style, which was done by a person called Kajio (who also directs the anime adaptation), is that of a super-deformed style, though it maintains a manly style to it through the use of heavy lining; the only odd thing is that every character looks to have "guylined" their eyes. In fact, this is where the "DD" comes from, as it apparently means "Design Deformation". At first it looks odd, but it's very fitting for this title and it's still very easy to identify every character, which is great. This simplified style does translate to the anime having flash-like animation, though, but here it also works so I can't complain. The music is mostly subdued, which fits with the modern-day world DD takes place in, though there are short uses of well-known FotNS songs, especially that of "Ai wo Torimodose", the show's first and most well-known opening. The voice work is well-done, though outside of Chiba no identifiable seiyuu are used; at least Kenshiro's voice does his "Atatatatatatatas!" well and Raoh's voice is appropriately threatening when needed. Overall the production value is simpler but it doesn't need to be anything special, honestly.
DD Hokuto no Ken is a very funny gag series based on the Fist of the North Star mythos, but unfortunately it's only best-enjoyed by people who are familiar with the story and characters up through the final fight between Kenshiro & Raoh (a.k.a. the original TV series). Thankfully, Discotek has fully released those 109 episodes across three boxsets, with all of FotNS 2 being released in one boxset this November, so buy them now and then look for DD Hokuto no Ken. You'll definitely love how Kajio takes these characters and fits them into a modern-day non-apocalyptic setting. Like the opening theme says, "There's No Need for Hidebu!"... Instead, go to Shin's host club and join in a group performance of "Lonely Lonely Lonely"!