Introduction
Minase is not a name you hear at every cocktail party, and that is precisely the point. Hailing from Akita Prefecture, this small Japanese independent has spent the better part of two decades perfecting a very specific kind of horological craft: case construction so precise that screws become invisible, and polishing so mirror-like it rivals the best from Grand Seiko or even Credor. The 7 Windows Yusai, reference VM15-M01TTB-SSB, is the brand's most literal expression of its philosophy—a dial with seven cutouts that reveal the beating heart of the movement, all wrapped in a case that feels like a piece of architectural origami.
I wore this watch for seven consecutive days, through desk work, weekend errands, and one very long dinner. I did not baby it. I did not polish it every night. I simply strapped it on and let it live on my wrist. What follows is a wear-focused review, because at the end of the day, a watch is meant to be worn, not displayed under glass.
The Yusai reference adds a layer of color to the 7 Windows formula—a deep, almost ceramic turquoise blue on the dial's outer chapter ring and the movement's visible bridges. It is not a loud color, but it catches light in a way that makes the watch feel alive. Combined with the seven windows, the effect is mesmerizing. But does it survive a real week? Let's find out.
Brand History
Minase is the watchmaking arm of Kyowa Co., a precision machining specialist founded in 1963 in Akita Prefecture, Japan. Kyowa's expertise in drilling, cutting, and polishing metal to micron tolerances led to the launch of Minase watches in 2005. The brand is best known for its 'Sallaz' polishing technique—a multi-stage hand-polishing process that creates distortion-free mirror surfaces—and for case designs assembled without visible screws, using a patented 'case-in-case' construction. This heritage is evident in every facet of the 7 Windows Yusai.
Movement
Inside the 7 Windows Yusai beats a Minase-modified ETA 2824-2. The base caliber is stripped, decorated with perlage, Geneva stripes, and blued screws, then fitted with a custom skeletonized rotor. Minase regulates each movement in-house to a tolerance of -3 to +5 seconds per day, which is tighter than the base caliber's standard spec. The movement offers 38 hours of power reserve at 28,800 vibrations per hour with 25 jewels. It is not an in-house movement, but the level of finishing and adjustment is far beyond what you would find in a standard ETA-powered watch. The seven windows on the dial allow you to see the balance wheel, gear train, and mainspring barrel in action—a constant reminder that this is a mechanical object, not a digital display.
Specifications
The case measures 39mm in diameter, 11.5mm thick, and 47mm lug-to-lug. It is crafted from stainless steel with a sapphire crystal and water resistance of 50 meters. There is no lume on the dial or hands, which is a deliberate choice to keep the focus on the movement and the polished surfaces. The watch comes on a leather strap with a pin buckle, though the SSB suffix in the reference suggests a stainless steel bracelet option is available. The clasp is a simple pin buckle, which I found secure and comfortable.
Wrist Feel
The first thing you notice when you pick up the 7 Windows Yusai is that it is not heavy. At 39mm across and 11.5mm thick, it sits low and flat on the wrist, with a lug-to-lug of 47mm that hugs even smaller wrists without overhang. The case has no traditional lugs; instead, the strap attaches to a recessed area between two polished facets, which makes the watch feel more like a cuff than a conventional round watch. The leather strap is supple and breaks in quickly, and the pin buckle is simple but secure. Over a full day of wear, I forgot I was wearing it—until I caught a glimpse of the dial and remembered why I was staring.
The Sallaz polishing is not just a marketing term. The case sides are so mirror-like that they reflect light in a way that makes the watch appear to change shape as you move your wrist. The edges are crisp but not sharp; Minase has chamfered every intersection so that nothing digs into your skin. The crown is small and tucked at 3 o'clock, easy to grip but never intrusive. On the leather strap, the watch balances perfectly—no top-heaviness, no sliding around. If you opt for the stainless steel bracelet, expect a bit more weight and a more formal presence, but the same comfortable geometry.
Accuracy
Over the course of my week, the watch ran consistently at +4 seconds per day, measured against an atomic clock app. That is well within Minase's stated regulation range and excellent for a non-COSC ETA base. There was no positional variance significant enough to notice; whether I left it dial-up overnight or crown-down, it stayed within a second of the same daily rate. For a watch at this price point, you might expect chronometer certification, but the real-world performance is more than adequate for daily wear. Just don't expect it to be a quartz-level timekeeper—it is a mechanical watch, and a few seconds per day is part of the charm.
Occasions and Wrist Presence
The 7 Windows Yusai is best suited for daily wear, dress occasions, and formal settings. Its 50m water resistance and lack of lume mean it is not a sports watch, but it can handle a splash or handwashing without worry. On the wrist, it commands attention because of the dial. The seven windows draw the eye immediately, and the turquoise accents add a pop of color that is noticeable without being garish. It reads as a piece of jewelry first and a timepiece second. It is not a watch for the shy, but it is also not ostentatious. It sits in that sweet spot where a fellow watch enthusiast will stop you to ask what it is, while a non-enthusiast will simply think you have excellent taste. I would rate wrist presence 4 out of 5—distinctive but not overwhelming.
Reference Variants
The Yusai is one of several colorways in the 7 Windows line. Other references include the VM15-M01TGN-SSB with a green dial, the VM15-M01TSL-SSB with a silver dial, and the VM15-M01TDB-SSB with a deep blue dial. All share the same case, movement, and seven-window layout, differing only in the color of the chapter ring and movement accents. The turquoise of the Yusai is the most vibrant of the group, but the others offer a more subdued alternative for those who prefer monochrome.
Investment Value
The Minase 7 Windows Yusai retails for approximately $9,500 USD. Pre-owned examples typically sell in the $6,500 to $8,500 range, depending on condition and completeness. Values are stable, but the brand is niche, so resale can be slow. Minase produces in very small numbers, and the 7 Windows is a signature model, so there is no risk of depreciation due to oversupply. However, this is not a watch to buy as an investment. Buy it because you love the craftsmanship and want something that few others will have. There is no major auction history for this model.
Service
Service interval is recommended every 5 years. A full service through Minase's Japanese workshop, including case refinishing and Sallaz polishing, costs around $600 USD. Because the base movement is an ETA 2824-2, any competent independent watchmaker can perform a standard service, but the case finishing requires specialized equipment. Minase recommends authorized service to maintain the mirror polish and case integrity.
Pros and Cons
Pros: Exceptional Sallaz polishing and case construction; seven windows reveal beautifully decorated movement; wears comfortably at 39mm with short lug-to-lug; limited production ensures exclusivity.
Cons: Water resistance only 50m limits versatility; no lume on dial or hands; base ETA movement may disappoint purists at this price; limited availability outside Japan.
Final Verdict
The Minase 7 Windows Yusai is a wearable sculpture that rewards close inspection. It is not a tool watch, but as a daily piece of horological art, it excels. If you value hand-finishing over brand cachet, this is a compelling choice. Over a week on the wrist, it proved comfortable, accurate, and endlessly fascinating to look at. For the sophisticated young collector who wants something different, the 7 Windows Yusai delivers in spades.
