AC Sanctuary’s RCM program has built a reputation for engineering the future into machines that manufacturers never intended to be this sharp. And while Nakamura-san was away hosting a track day for RCM owners and their devastatingly fast specials, Akito-san took the time to note down the details of their latest resurrection: RCM-643, a Kawasaki GPz1100 reborn with purpose, precision and far more capability than its early-’80s frame ever dreamed of. For a bike long respected as the “last real Z,” Sanctuary treated it less like a restoration project and more like a platform to showcase everything their modern chassis philosophy can wring out of an air-cooled icon.

If you ever rode a stock GPz1100, you’ll know exactly what Sanctuary were up against. Kawasaki’s final air-cooled Z engine was a brute, torquey, full of midrange, and eager to shove itself down the road with a hard mechanical pulse. But the chassis simply wasn’t up to the same standard. Heavy, soft, and built for high-speed touring rather than corner-carving, the GPz1100 resisted direction changes with all the enthusiasm of a freight train. Sanctuary themselves admit the bike “just wouldn’t turn,” even when Nakamura rode one decades ago. The mission for RCM-643 was simple: keep the engine’s soul, eliminate the compromises.

There are custom shops, and then there’s AC Sanctuary, a name that has become synonymous with the kind of meticulous, borderline-religious craftsmanship that makes purists weak at the knees. In Japan, their famous parts catalogue is known as 'The Bible', and you start to realise just how admired the outfit really is. Their latest masterpiece, the RCM-696 Z1-R, is not just a resto-mod. It is the physical embodiment of 30 years of evolution, experimentation, and that stubborn Japanese perfectionism that refuses to settle for “good enough.” Built for a client from Gunma Prefecture, this Kawasaki Z1-R represents the latest iteration in Sanctuary’s long-running RCM (Real Complete Machine) program, and it’s nothing short of sensational.

At first glance, it’s unmistakably a Z1-R, but one that has been sharpened, tightened, and tuned in every conceivable way. The all-new upper cowl mount, crafted from machined duralumin, is a feat of modern engineering. It allows millimetre-precise adjustment in every direction: fore, aft, up, down, tilt, and even light axis. Nakamura-san, the obsessive genius behind Sanctuary, jokes that the bracket kit might be overkill, but that’s exactly why it works. The cowl itself sits close to the steering head, avoiding that “turtle neck” look some frame-mounted setups suffer from, yet maintains full lock-to-lock steering. It’s functional beauty, executed with surgical precision.

There’s a certain magic in the way Kengo Kimura from Hiroshima’s legendary Heiwa Motorcycle approaches a build. It’s not about throwing every aftermarket part in a catalogue at a bike, but rather stripping it back, distilling it, and then rebuilding it until every line looks intentional and every weld feels inevitable. His latest creation, 250TR No. 018, is no exception. Based on a humble Kawasaki 250TR from the early 2000s, this custom scrambler is a masterclass in minimalism and balance, drenched in a rich metallic green that practically glows under the workshop lights.

Kimura-san has become something of a cult figure in Japan’s custom scene. Over the past two decades, Heiwa Motorcycle has built a reputation for bikes that are understated yet dripping with style, often leaning into brat and tracker aesthetics with a distinctly Japanese flair. This latest build, completed just this week, continues that tradition, taking Kawasaki’s factory retro-trail bike and turning it into a lean, purposeful machine that could just as easily win a design award as it could tear through Hiroshima’s backstreets. And as part of Kimura-san's more affordable range of bikes, it allows his fans to ride a Heiwa every day, without selling a kidney for the privilege. 

It’s no secret that Kawasaki’s Z900RS has become a darling of the custom scene in Japan, with the home grown product proving incredibly popular with builders and their clients. So, it made perfect sense that come show season, Japanese motorcycle parts distributor Plot, would use a Z as the canvas to show off many of the products they sell. But to push things into truly legendary territory, their latest creation takes the beloved retro roadster and channels the spirit of Kawasaki’s late-’70s square-tanked bruiser, the Z1000 Mk.II. And just like the factory evolution from the round-tanked Z1 to its boxier successor, this custom packs in refinement, precision, and a deep respect for history. 

Plot is an absolutely enormous presence in the Japanese motorcycle scene and they use custom bikes to show off exactly what the business is all about. Not only do they distribute OEM pieces, and all of the parts you need to service or restore a bike, they're also the national distributor for a huge number of local and international companies. From massive brands like Brembo, to small Japanese businesses that produce small runs of custom parts, it can all be found in the warehouses of Plot, ready to be shipped around The Land of the Rising Sun.

It's the 1970s and the engine war is over, the British twins have been killed off and the motorcycle world is all about the multi-cylinder. Kawasaki was one of the manufacturers responsible for that gigantic shift and the Z1 was emblematic of this new and exciting era. So, what on earth was the big green company thinking, when in 1976 they introduced an all-new KZ750, with of all things, a parallel twin as the powerplant? Well, their reasoning was sound at the time, but victims of their own marketing, the bike failed to sell. But if Kawasaki had seen this modern interpretation and met the enthusiastic man behind it, things might have been very different. Meet American Victor Wilkens and his 1980 Kawasaki KZ750 Twin, a custom motorcycle that proves you get a hell of a result when you know exactly what you're working with.

Back in 1976, from Kawasaki's point of view, the production of a big twin with the styling of the famous Z series of motorcycles made a lot of sense. To the big Japanese manufacturer, they were offering to the public big bike looks, with solid performance, good reliability, easy maintenance and all at a cheaper price than some of their competitors' much smaller offerings. It wasn't the full-blown four-cylinder, but it was a damn good bike. But the public didn't buy it, they'd bought into the hype of multi-cylinder machines and although Kawasaki made a solid sales pitch, the 750twin just never sold in big numbers, ending its run in 1983.

We've been blessed in recent years, with the big Japanese workshops producing one incredible resto-mod after another. In what has turned into an all-out arms race, some of the world's biggest suppliers of aftermarket components have teamed up with various customisers, to take these machines to previously unimaginable levels of form and function. But it would be misleading to think this is a new trend. All the major players we've featured have been in the game for a hell of a long time, and as if to prove the point, this particular Kawasaki Zephyr 1100RS is more than two decades in the making. Its builder, Shabon Dama, calls it the 'ultimate incarnation' of a '90s road bike, and we can't get enough of this barnstorming blue beast.

Like many of their contemporaries, Shabon Dama has been plying their trade for a very long time, with some of their employees approaching retirement age, although showing no desire to quit anytime soon. They have followed the well worn path, focusing largely on a small group of motorcycles from one manufacturer, offering a range of their own parts built under a number of unique brand names, and slowly expanding from backstreet heroes to global domination. But like anything done to a high standard, good things take time, and manager Takigawa-san remembers his first interaction with this particular build. “This navy blue bike is owned by someone who has been coming to us for more than 20 years. He originally came to our shop for a carburettor change.”

The Japanese street racing scene has largely been known for the 300km/h Midnight Club and their flashy two-wheeled rivals, the Bosozoku, who always preferred looks over speed. But if you get to talking to the older motorcycle tuners in the Land of the Rising Sun, their inspiration comes from a much lesser-known group that preceded them all, the Kaminari-zoku. The 'Thunder Tribe', like their British and American biker brethren, were post-war outcasts who loved riding their motorcycles as fast as they possibly could on public roads. The times may have changed, but Iwaki city's MG-Nest is heavily influenced by that gritty brat era and their penchant for huge horsepower. This Kawasaki KZ1000 is the personal machine of head honcho, Takanori Shiine, and it's a perfect mix of ferocious speed and a punk rock personality.

The team at MG-Nest are 110% dedicated to building ultra fast Z bikes, and they're not just quick on the street. The same engine package as used in this bike has been fitted up to motorcycles competing at the Taste of Tsukuba event at the famous circuit, by clients racing in the JD-Ster drag racing series around the country, land speed attempts and just about any other way you could think of if you have a serious need for speed. So, how does Shiine-san use his bike? "I'll use it for anything," he smiles. And he means it, as you'll come to discover, this motorcycle with its brat looks and almost run-down aesthetic, is capable of mixing it up with just about anyone racing in an air-cooled class.

The resto-mod scene is booming in Japan with thousands of '70s and '80s superbikes having been transformed into big dollar, bulk horsepower machines while retaining their iconic, classic silhouettes. The likes of AC-Sanctuary, Bull Dock, Bagus and American Dream lead the charge, and they don't just build the bikes, each shop also has a catalogue of incredible parts and in-house brands, that they've developed to produce everything you could possibly need to transform your favourite Japanese retro ride. But after twenty years of friendly rivalry, the arms race has reached a new stage, and firing the first shot, Bull Dock has come out swinging in a big way. Meet their latest creation, a Kawasaki Z1R, in full GTM spec and packing a 1260cc billet engine to take horsepower levels to all new heights.

Most of these shops have been running for well over twenty years, and in the early days, it was without a doubt the original Z1 and early Z900s that proved to be the most popular donor for a full resto-mod conversion. It's easy to see why, even more than fifty years on it is still one of the most beautiful bikes ever built and has increasingly become a hell of a collector's item. But as the workshop owners have told us over the last 12 months, finding donors of these classics is becoming nearly impossible, stock has simply dried up, and the value of a good original is too high to contemplate cutting one up. There are also those who prefer the more muscular lines of the later Z1000 machines, and then there is another reason the big capacity bike has become so popular.

It's as close to being the Academy Awards of our industry, there are many other amazing events, but there is a prestige to the Yokohama Hot Rod Custom Show, that means for many builders, simply being invited to exhibit is a lifelong goal. Each year's event is awash with incredible creations and it also serves as a stark reminder that when it comes to the Japanese scene, the rest of the world is really only getting a small glimpse behind the curtain. So, what better way to lift the lid on one of the nations best builders, who is largely unknown outside of Japan, than to show off his most recent trophy winning creation. Kenta Onishi is the boss at Eccentric Motorcycles, and this wild in white 1997 Kawasaki Estrella took out 'Best Domestic Bike' at the recent 2024 Yokohama show.

Onishi-san is a custom bike builder known for never following a trend, to the point that when a certain style is in vogue, he will avoid it like the plague. His small shop in the city of Kawaguchi has always been a place for those looking for something truly different, as a shared creative process between client and creator is truly encouraged. Onishi-san takes his job very seriously, and before putting pen to paper to create a design, he will often spend months studying the style and its history. For this build, his client wanted a custom that drew heavily on pre-war automobiles, while also incorporating plenty of Art Deco touches.