The Bonding Sickness is a sickness/disease that affected both humans and their spirit animals, caused by bonding without the Nectar of Ninani. The bonding sickness is different for everyone. It was a pandemic that spread after The Evertree was damaged in the first Devourer War. It was most common in Stetriol due to the island not having access to the Nectar, leading to the creation of the Bile; it cures the bonding sickness, but the trade off is being a prisoner of its effects and Gerathon the Serpent's mind-control. When the Bile was introduced to Stetriol, the islanders took it, mistaking it for a blessing.
If the bonding sickness is not cured, the victim will become extremely sick or insane, which is sometimes followed by death. People were freed of the bonding sickness when the original Evertree was destroyed by the Great Beasts in The Evertree.
- Aidana: Aidana developed the bonding sickness soon after bonding naturally (without the Nectar) with Wikerus the Raven. She became sick to the point of hallucinating frequently, and Wikerus became unstable as well. When she was given the Bile by Zerif, she was on the verge of death.
- Drina: Drina bonded naturally with a spider named Iskos and developed the sickness. She was bedridden, and often had violent mood swings because of it.
- King Irwyn: Irwyn developed the bonding sickness, and then killed his spirit animal in hope that he would be cured. However, the sickness only became worse.
- Shane and Drina’s mother: It was mentioned in The Book of Shane that Shane’s mother had the bonding sickness.
- Ifa: A character in Tale of the Great Beast Ninani who becomes sick due to her bond with a chinchilla named Cachi. She later dies because of it, although her death leads to the discovery of the Nectar.