Kaiyō is not a distillery but a bottler founded in 2017 by a former Asahi executive. The company sources distilled malt whiskies from Japanese distilleries and matures them in a distinctive way: handcrafted Mizunara oak casks, the rare Japanese oak that challenges coopers due to its delicate grain structure.

The Mizunara Oak is Kaiyō's flagship and catalysed the Mizunara movement in Japanese whisky. What sets this bottling apart is its three-month maturation at sea—casks depart Osaka on a ship crossing international waters before the whisky is bottled. This maritime phase imparts subtle complexity to the finished spirit.