Japanese Watchmaker Otsuka Lotec Presents the No.5 KAI, With Satellite Hour Display

A not-so-young-brand that only appeared recently on the international scene and an independent watchmaker that we’ve named Japan’s new sensation, Otsuka Lotec is the brainchild of watchmaker Jiro Katayama. Even though these watches are extremely hard to get outside of Japan (yes, that means pure JDM coolness), the brand has started to gain recognition and fame, specifically with its two fascinating models that are the No.6 and the No.7.5. And we should not forget that Katayama-San teased in an interview its next creation, the No.5 KAI with wandering hours. And we’re happy to tell you that it’s now finalized.

Otsuka Lotec’s founder Jiro Katayama continues to explore exotic displays based on a simple automatic movement, with steampunk, industrial designs. Following the retrograde indications of the No.6 and the jumping hours and disc-based indications of the No.7.5, it is now time for another unusual indication of the time to be presented, the satellite or wandering hour display. Yet, we have to remember that the No.5 watch is not new and was first launched 12 years ago. However, while the new model can be presented as an evolution of the older watch regarding its case design, the dial and its indications have nothing in common with the old model, which was a regulator-styled watch – some details on this page.

The new watch, the Otsuka Lotec No.5 KAI, retains the overall and nonconformist shape of the lineup, with a 40.5mm diameter and a three-dimensional shape with high-profile box sapphire crystal, with the case edge lowered to the maximum extent. The case thickness is measured at 7.6mm, while the watch is 12.2mm – just to give an idea of how protruding the crystal is. The case, made in steel, is finished in the classic way of Otsuka Lotec, meaning deliberately rough and industrial, with straight-grained surfaces all around. The caseback is solid steel and the water-resistance rated at 30m.

Looking through that massive sapphire box, you’ll discover what’s really new with the Otsuka Lotec No.5 KAI; the in-house satellite hour module. Mounted on top of an outsourced automatic movement, it relies on 3 rotating discs (each with 4 hours), themselves driven by a central carrousel rotating on its own axis. Each hour satellite travels on a 120-degree arch for an hour, thus pointing the minutes on this track. To prevent the backlash characteristic of the satellite hour mechanism, the hour disk is driven by a double reduction gear. Also, two ball bearings are clearly visible on the dial side; one is used as a roller to engage the hour disc and rotate it in its next position, allowing for instantaneous switching twice per hour, similar to a jumping hour mechanism; the second is positioned at the centre of the seconds’ disc.

Fun fact: the Otsuka Lotec No.5 KAI relies on two Japan-made ball bearings from MinebeaMitsumi. The ball bearing used for switching the hour disk was specially made for the No.5 KAI. The other one, found at the centre of the seconds’ disc, was first seen in 2015 and is still, at 1.5mm in diameter, the world’s smallest of its kind. Otsuka Lotec has also slightly revised the satellite display with modern wristwatches in mind, specifically to be worn partially hidden under a cuff and still be legible.

Power comes from a classic Japan-made Miyota 90S5, an automatic movement with 25 jewels, a 4Hz frequency and about 40 hours of power reserve. It is used to provide power to the in-house module on top. The watch is worn on a double-padded black leather strap, closed by a pin buckle.

As with other watches from the brand, the availability of the Otsuka Lotec No.5 KAI remains difficult and is limited exclusively to Japan. It’ll be offered through a lottery scheduled for March 2025 at JPY 748,000 (tax included), so about 4,625 Euros. For more details, please visit Otsuka-Lotec.com.