The Glow is a weaponized form of emotions created by Gideon Graves that uses Subspace to trap someone inside their own mind with their personal demons. It is first seen on Ramona Flowers at the end of Scott Pilgrim's Precious Little Life and continues to appear throughout the series. Its nature remained a mystery until Scott Pilgrim's Finest Hour, where Gideon explains its purpose to Scott and Ramona. When active, the Glow will cause the heads of those affected to literally glow, hence its name.
The Glow Pt.2 is an album by The Microphones. The chapter The Glow Pt.2 was named after it.
Described as a powerful weapon of "emotional warfare", the Glow manipulates the Subspace inside the minds of those it infects, causing them to become overwhelmed by their personal issues. The Glow suppresses positive emotions such as friendship and love, and simultaneously enhances negative feelings like suspicion, jealousy, and self-loathing. As such, the Glow can be used to poison or destroy relationships. It also makes a person more susceptible to Gideon's manipulations. Gideon demonstrates this when he uses the Glow to make Scott and Ramona argue during the final battle.
It appears that the Glow can lie "dormant" inside the mind of an infected person after the effects of their initial exposure wear off, as evidenced by Ramona's (and later Scott's) frequent episodes of spontaneously sporting the Glow throughout the series. The Glow is triggered by intense emotional moments, like in Volume 5 when Ramona is faced with the prospect of Scott having cheated on her with Knives, and is also experienced by Scott in Volume 6 after Kim points out the mistakes he made while they were dating in high school (namely beating up Simon Lee and leaving for Toronto without telling her). The effects of the Glow will eventually wear off, but the only way to get rid of it permanently is for the inflicted to actually come to terms with their personal issues.
While Gideon is able to spread the Glow via touch, he can also fire it at people in a projectile form as demonstrated when he sprays the crowd at Chaos Theatre with it in the final book. Gideon, himself, is immune to the Glow since he has already been trapped inside his own head since childhood and (in his opinion) has no personal issues to deal with.
One unintended side effect of the Glow is that it can be utilized by certain afflicted people to access Subspace whenever and wherever they wish. Ramona found a way to use the Glow to escape conflicts and intense moments, such as when she first left Gideon, and also when she leaves Scott at the end of book 5.
The Glow was created by Gideon, and was first tested on Ramona to seal her inside the subspace of her own head where Gideon was godlike. Ramona was able to harness the Glow, however, and use it to access Subspace and escape. Part of Gideon's control remained inside her, possibly because of the Glow. Later in the series, Scott is seen with the Glow, and it threatens his relationship with Ramona. Scott is first seen with the Glow when he sees Roxie Richter walking down from Ramona's room after being chased through Subspace by Mr. Chau.
Initially, Scott thinks he is the only one who sees the Glow on Ramona. However, in Volume 5, Kim Pine tells Ramona that her head is glowing and even takes a picture of it with her cell phone. Ramona is surprised and claims she's never noticed it before. She does, however, hint that she knows what it is. Later on, the Twins also mention the Glow, implying that it is something important, but don't reveal what it means.
Towards the end of book 6, Gideon finally explains the nature of the Glow to Scott and Ramona, and uses it in an attempt to turn them against each other in their final battle. Scott, however, is able to free himself of the Glow's influence when he confronts Gideon inside the subspace of Ramona's mind and headbutts him whilst sporting the Glow. Though the Glow does not affect Gideon (who is already trapped within his own mind), Scott's actions weaken Gideon's hold over Ramona, allowing her to sever her remaining ties with Gideon and cast him from her mind. She and Scott then proceed to defeat Gideon in the real world, ending him once and for all. With Gideon dead, the Glow is presumably gone for good.
While unclear, there are several possibilities as to how and when Scott contracted the Glow. He was either infected intentionally by Gideon, or it was transferred to him by Ramona (perhaps by accident). Since the Glow is first seen emanating from Scott's head in Book 4, either possibility is acceptable, especially since Scott encountered both Gideon and Ramona in Ramona's Subspace, creating ample opportunity for transfer at said point. Scott also might have been susceptible to the Glow after traveling through Subspace on multiple occasions.
- Gideon claims the Glow is what has made him his millions. It is not clear, though, if this means he sold the Glow to other people, or if he used the Glow to manipulate people into buying his company's products. The latter is more likely, since Gideon is the only one who knows how to fully control the Glow.
- Early in the series, fans believed the Glow was meant to be an inside joke or just another part of Ramona's character. However, as the series progressed, it became clear that the Glow was something important to the story.