Altruism, the psychology of helping others. I figured this would be a good topic to start on for the challenge. Altruism is the unselfish desire to help others. There are many theories about why people help each other, and in what situations are more likely to produce helping behaviors than other situations.
So you have your character. Maybe they are the type of person more likely to help. Or perhaps they are in a situation where they are the only person available to provide help. Each character could have different reasons for helping another character out. The different motivations for helping can make for different courses of action in the scene and consequences for the characters.