The Bonding Sickness is a sickness/disease that affected both humans and their spirit animals, caused by bonding without the Nectar or Bile. 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. The Bile cures the bonding sickness, but the trade off is being a prisoner of its effects and Gerathon's mind-control. 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. When the Bile was introduced to Stetriol, the island took it, mistaking it for a blessing.
- King Irwyn believed that killing his spirit animal would cure his bonding sickness, however it only made it worse.