Chuhai is a cocktail containing the Japanese alcohol called shochu, soda, and any kind of fruit juice. In Tokyo area we sometimes call it Sour instead of chuhai. This cocktail is very popular in Japan, commonly served in izakaya-style restaurants and restaurants that cater to Japanese salary workers.
Combine club soda, shochu, simple syrup, and yuzu extract in a glass and mix well.
Add ice cube and Korean citron tea (optional) and mix well.
Garnish with a slice of lime, and serve immediately.
To Make Simple Syrup
Bring the water to a boil in a small saucepan. Dissolve the sugar into the boiling water, stirring constantly. Once the sugar is dissolved completely, remove it from heat and let cool completely and thicken.