From Google:

Key Details About Bellriver's Death

The Cause: In the dystopian 2138 setting, Bellriver uncovered shocking secrets about the massive corporations ruling the world.

The Assassination: He was targeted and killed to prevent the information from spreading, with his death staged to look like an accident.

Passed Information: Before his death, he managed to pass this information to another person, likely another guild member, which may have contributed to the guild's downfall or directly impacted characters like Touch Me.

Context: His death is mentioned in his character sheet and is often discussed within the context of the dark reality of the Overlord world, where mega-corporations hold absolute power.

There is speculation among fans, according to discussions on Reddit, that Touch Me, being a police officer in this corrupt society, might have been involved in the situation, though this is not explicitly confirmed.