Try to press the A button when this marker is on one of the clear icon to fight the bully chao. During the fight, you will see a marker with dark and clear icons.
Occasionally, your chao will get into a fight with a bully chao. This stage usually lasts for approximately 1 hour, but you can speed up the process by feeding your chao fruit.
Once they hatch out of their egg, they are known as child chao. As you may already be aware of, chao will go through different stages of their life.