A lot of Muslim brothers and sisters in Japan believe that all types of teas are halal. Unfortunately, it is not the case. They have to be careful in choosing which product to consume and which one to avoid. The ingredients these food factories use for making these products are, in many cases, totally unexpected.
For example, this Premium Earl Grey Tea Latte is not halal as it contains pork-based emulsifier. Please stop using it at any cost. We need to understand full well that not all soft drinks, juices, and teas are halal. You may want to confirm each and every single product before consuming any item in Japan.