Square Window Envelope + Card: Great for sending invitations or photographs showing images/texts from the window on the envelope - these suckers would be custom tho / would need to find the most cost affordable way to produce these.
This is a traditional japanese Tenugui. ( Tenugui is a piece of dyed cotton cloth. ) Almost everybody uses stationery. How it is used depends on each individual. This item becomes unique and special to him/her. With that as the motif, “stationery cloth” was made.