No, 'Informer' is not based on a true story. It's a made-up narrative crafted by the author's imagination, but it may touch upon themes or concepts that are relevant to real life in some way.
The first informer in Chinese history could be traced back to the Spring and Autumn Period, and it was said to be Shen Buhai. Shin Buhai was an intelligent politician and informant who lived in Korea in the middle of the 5th century B.C. He successfully promoted the reform of Korea through whistle-blowing and strategy, becoming one of the famous politicians and whistle-breakers in ancient Chinese history.
The 'the informer true story' is likely about a real - life situation or events related to an informer. It could be about a person who provided information in a particular context, perhaps in a criminal case, a historical event, or some other situation where someone had inside knowledge and shared it.
There could be the person or group being informed upon. Their reaction to the betrayal, their attempts to defend themselves or seek revenge, are important aspects of the story. For example, if it's a political group being informed on, their members might fight back against the informer and those who support him. And there might be a detective - like figure who is trying to figure out who the informer is. This character adds an element of mystery and investigation to the novel as they piece together clues.
I have uploaded chapters 124 - 153 of the Ringbearer manga to the attachment. You can download and view it. Please note that this manga only contains 153 chapters because 124 chapters have not been released yet.