Special mission investigator who is tied up and gang raped and falls into pleasure

I work as a member of a "undercover security organization" that was formed secretly to eradicate crimes that occur in the underworld... While this organization is capable of extrajudicial investigations, it is a literal "undercover organization" that the state does not officially recognize, so it is not allowed to fail the operation. Six months ago, I was on the mission to investigate a gang rape case and get a full picture of the criminal group behind it. He then succeeded in following one of the crime group and reached the center of the organization's hideout, but...