The Glow Card has the ability to create glowing lights that look much like hundreds of fireflies. It is one of the most mild-mannered cards, not creating distress or panic to anyone before its capture, but forming into a pretty view instead. Its main body is the same as depicted in the card: a small, green fairy holding a dandilion flower. The Glow is under The Light.
The Glow was captured in Episode 18. Sakura first encountered it in a prophetic dream where a small fleck of light rests on her finger. She forgets the dream initially, but then remembers it when The Glow casts a small speck of light to fall on Sakura's finger during the festival at the Tsukimine Shrine. The Glow then was captured by Sakura with no resistance.
The Glow is transformed into a Sakura Card during Episode 67. Eriol had conjured a horse that cut the electricity to all the lamps to the Tsukimine Shrine during a festival. After Sakura and Syaoran subdued the horse with the combined effort of Syaoran's magic and The Thunder, Sakura uses The Glow to reilluminate the Shrine while the festival is still underway.