If you have any questions about the Japanese sizes, please check the size chart of each item and compare it with your home country’s size chart, for example here. Or measure a fitting shirt of yours like this and compare it with the dimensions displayed. As a rule of thumb: Asian sizes are one size smaller than their western counterparts. A Japanese size XL is roughly the equivalent to a European size L.
Most items have a pre-order deadline of December 14, so please check the product page for details.