Substitutes:

• Japanese Whisky: You can use any type or brand of Japanese whisky you like to prepare this cocktail. If you can't find any Japanese Whisky, you can use Scotch as a substitute. It has a similar flavor profile, although it might be slightly smokier depending on the brand.
• Fresh Lemon Juice: Freshly squeezed juice is always the best option, but bottled juice will work as well if you’re out of fresh lemons. Lime juice can also do the trick.
• Yuzu Juice: Fresh Yuzu is hard to find and expensive, but don’t worry: this recipe has been written so it can be made using bottled Yuzu juice. Yuzu purée can also be a good alternative; in both cases, make sure to have a high-quality juice or a purée (100% yuzu).
• Kuromitsu: Kuromitsu is a black sugar syrup made from unrefined sugar. It is usually available in Asian grocery stores, or you can make your own at home using “kurozato” or “kokuto” sugar (also available in Asian grocery stores or online). If you don’t have access to an Asian grocery supplier, don’t worry: you can replace it with cane molasses or make your own version using Muscovado sugar or any kind of dark brown sugar. In any case, this substitute syrup should be quite rich, so start by mixing 2 parts of sugar of your choice with 1 part warm water. Stir until the sugar is fully dissolved, and add more water if you’d like a lighter, less concentrated syrup.
• Egg White: If you're vegan or allergic to eggs, you can use aquafaba (the liquid from a can of chickpeas) as a substitute. It froths up just like egg whites and is flavorless. Pasteurized egg white is also a suitable option; in that case, use ½ oz as a substitute for one egg white. Shake twice just like you would if using regular egg white (see instructions above).

Making it Non-Alcoholic:

• Whisky Substitute: Use a non-alcoholic substitute; these are available and reasonably mimic Whisky's flavors. You can also use Mugicha, a traditional Japanese barley tea, as a substitute for the whisky: simply infuse it in hot water for at least 1 hour and let cool down to room temperature before using.
• Proceed As Usual: Use this non-alcoholic substitute instead of the regular Whisky, follow the original steps, and enjoy a non-alcoholic version.

Making it Vegan:

• Egg White Substitute: Use ½ oz of aquafaba (the liquid from a can of chickpeas) instead of egg white. It froths up just like egg whites and is flavorless.
• Proceed As Usual: Use this vegan substitute instead of the regular egg white, follow the original steps (for best results, aquafaba should be shaken twice as well), and enjoy a vegan version.