Founded in 1881 in Tokyo, Seiko is one of the few truly integrated watch manufactures in the world — designing and producing its own movements, crystals and cases entirely in-house. The Prospex line is the brand's dedicated sports collection, and the Sumo holds a special place within it as one of the most characterful and capable Japanese dive watches ever made — substantial, bold and instantly recognisable.

The Seiko Prospex King Sumo, reference SPB321J1 is a well-executed 45 mm stainless steel professional dive watch with a beautifully structured blue gradation dial — a finely pressed pattern that shifts from deep navy to a lighter, ocean-inspired blue, giving it real depth and visual character. Applied LumiBrite hour markers and hands ensure excellent legibility underwater, with a date display at 3 o'clock and the screw-down crown positioned at 4 o'clock in true diver's fashion. The dark blue ceramic unidirectional bezel is a meaningful upgrade over earlier aluminium versions — scratch-resistant and fade-proof, it is built to last. At its heart beats the Seiko Calibre 6R35, a robust in-house automatic movement with manual winding capability, 24 jewels, running at 21,600 vph with an impressive 70-hour power reserve. A sapphire crystal protects the dial, while the Super-Hard coated case and bracelet add exceptional scratch resistance. Water resistance is rated at 200 metres, backed by a screw-down crown and caseback. The watch is fitted on a three-row stainless steel bracelet with a modern milled folding clasp and one-push diver extension.

This King Sumo is in near mint condition and comes as a full set.