Myeongdong has two Daiso stores: Main Store (43 Myeongdong-gil) and Myeongdong

Station Store (134-1 Toegye-ro), both 10 AM–10 PM. Character stationery can vary by store, so try the other one if you can't find it. The Miffy gel pen 0.48mm (2-pack, 3,148 orders) writes in black, nice for a trip diary.