Looking for a Japanese comic, a group of people take a bus to travel to the mountains. Why are they trapped and unable to make a sound, or why is there a black monster often appearing around them?

1. Attacked or kidnapped by unknown creatures: A group of people are attacked or kidnapped by unknown creatures while traveling. In order to prevent being discovered, they must stay quiet and not shout loudly. Typical works are like "Slime Taro".

2. Being involved in a mysterious space: A group of people are transported or involved in a mysterious space through some strange way. Making noise there will cause danger, so they must be quiet. For example, the "silent space" in "Death Note".

3. Encountering a wraith or curse: If a wraith or curse is triggered in a certain location, you must keep quiet. Making loud noises will cause disaster. Such as the curse of the mountain village in "Heartbeat Echo".

4. Trapped by an unknown experiment: A group of people are inadvertently involved in a mysterious experiment conducted by an organization. They must stay quiet to avoid the failure of the experiment. This kind of plot is more commonly used in science fiction and suspense works.

5. Suffering from a strange disease: A certain virus or disease that causes people to make noise will have dangerous consequences, so they must be silent. Similar to the parasite virus in "Parasite".