Seiza Sitting, For The Win!
If you go to Japan, you should at least expect to sit in the popular Sieza sitting position, as it is quite the common way of sitting. The position requires one to sit ON their legs and is a position used during several ceremonies and rituals. All this can present challenges for foreigners.
The Seiza sitting position requires a level of flexibility that one has to master before it is comfortable to sit that way for extended periods. If this position is TOO hard, you still have the option of crossing your legs in front. In theory, both are easy to execute, but this is not the reality when put into practice, making it difficult for foreigners to participate in ceremonies properly.