The Citizen Tsuki-yomi A-T BY1010-81Z takes its name from Tsukuyomi, the moon deity of Japanese mythology — fitting, because this is the world's first watch to unite a moonphase display with radio-controlled atomic timekeeping. It's the kind of engineering-first flex that only Citizen's Tokyo watchmakers deliver: a dial styled after the lunar surface, a moonphase window at 6 o'clock tracking the real sky above you, and a movement that syncs to atomic time signals so the whole display — day, date, perpetual calendar, world time across 24 zones — stays dead accurate without you lifting a finger. The deep purple dial is a masterstroke, shifting from near-black to rich violet in the light, cut through with silver-tone hands and black accents for serious legibility.
The 43mm case and bracelet are forged from Citizen's proprietary Super Titanium™ — surface-hardened to be five times harder than stainless steel yet roughly 40% lighter, so a watch this technical wears with almost startling ease. Sharp faceted edges catch the light like polished armour, a scratch-resistant sapphire crystal guards the dial, and 100m water resistance handles real life. Powering everything is Eco-Drive calibre H874, converting any light into perpetual energy — no battery, ever. This is Japanese watchmaking at full stretch: mythology on the dial, metallurgy in the case, atomic physics in the movement.
Please note that the radio-controlled functionality will not work in Australia due to the absence of radio transmitting stations within range. These stations are exclusive to four regions: Europe, USA, China and Japan. However, this does not affect manual time adjustment.
What we love about this watch - We love that the BY1010-81Z is a genuine world-first you can wear every day. A moonphase complication paired with atomic accuracy and a perpetual calendar means the most poetic display in watchmaking never needs correcting — set it once and it's right for decades. The purple dial is the collector's pick of the Tsuki-yomi range, and the Super Titanium construction makes a 43mm watch feel like half its size on the wrist. Serious technology, zero maintenance, endless conversation. Product code: BY1010-81Z.
