No. 5 KAI

The No. 5 KAI is a mechanical watch from Ōtsuka Lōtec, the Tokyo watchmaker founded by Jiro Katayama. Introduced in 2025, it has a steel case and a leather strap, but no ordinary hour or minute hand. Numbered discs carry the time around its face. Much of the machinery that moves them is left in view.

Katayama worked in car and product design before making watches. His original No. 5 appeared in 2012 with a different display: separate hands for the hours and minutes, plus a date. The KAI keeps elements of that watch's construction while changing the way the time is shown.

Three discs share the job. Each carries four hour numbers and travels around the center of the watch. The number nearest the curved scale on the right tells the hour; its position beside the scale tells the minutes. A 5 alongside 45 means 5:45. At the end of that hour, the 5 leaves the bottom of the scale and the 6 arrives at the top. This is called a satellite-hour display.

Ōtsuka Lōtec gives a practical reason for putting the scale on the right: a jacket sleeve can cover part of a watch. Collecting the hours and minutes at the exposed edge is meant to leave them readable.

Underneath is an automatic movement made by Miyota, which supplies power to Ōtsuka's own display mechanism above it. The wrist's movement winds the watch. The numbered discs have to travel around the face and also turn individually, bringing a different hour into position for their next pass.

A small roller helps make that change. As a disc meets it, the disc turns to its next position. A ball bearing lets the roller turn freely: tiny balls move between its inner and outer rings. MinebeaMitsumi made this bearing specifically for the job, only 2.5 millimeters across. A separate bearing supports the seconds disc near the bottom. The supplier says these parts are made by specialist technicians, including hand assembly.

The tall sapphire cover leaves the display visible from the side as well as the front. Beneath it, plates and numbered discs sit at different heights; there are gaps and shadows between them. The watch is 12.2 millimeters thick overall. The raised cover makes room for the machinery above the steel case, so the discs remain visible even when they have moved away from the scale.