The BT21 café is based on the BT21 character brand, a collaboration between South Korean boy band BTS and LINE FRIENDS. The cafe opened for a limited period in Omotesando, Shinjuku and Shinsaibashi back in summer, and due to its popularity it's set to open once more in Shibuya (Tokyo) and Umeda (Osaka). The café is reservation-only. Those who do book a table can look forward to getting their hands on one of the above clear files. Reservations began on October 17 at 12:00 (JST), so be sure to…