The Light Pen (光筆 Hikari Pen) is a Magic Item.
The Light Pen takes the form of a normal-looking, light-colored pen with an arched clip, with its end adorned with a small sphere. In the manga, the barrel seems to be adorned by a writing, which, however, isn't well discernible. Its most distinctive trait is its glowing nib, which is light, prominent and somehow rounded in appearance, made of unknown material which allows the pen to use its special ability.
The Light Pen is a tool that enables the user to write in the air around them. There are a variety of colors, with 72 being currently available.