Guilt

As they entered the office, Bai Rouyun leaned against the wall and looked at the big stone basin in the middle.

This stone basin was the most common communication device on the continent. It was full of water, and one would pour a specific mixture of herbs and ground-up ores into it, which had previously been infused with a person's soul imprint.

It was the soul imprint that made it so that you contacted the right person; the ingredients alone could not connect the two communication devices with one another.

This had one downside. They would have to get the powder from the person, and when it had been used up, they would once more have to meet the person they wanted to contact to stock up on the powder that was infused with their soul imprint.

It was also because of this that Bai Mulan had barely contacted his friend throughout the many years he had been on the prison continent.