What is Blackmail manga?

In general usage, blackmail is a crime involving unjustified threats against a person or organization in order to make a gain or harm or cause material loss to them unless a demand is met. It may be considered similar to or a form of extortion, although some jurisdictions will consider them as separate crimes. Most often, blackmail involves the threat of revealing some secret to a given third party, which may be another person, a rival organization, or a state institution such as the police, or to the general public. In anime and related media, and more specifically in pornographic works, blackmail is also a device used to coerce people, generally female and often schoolgirls, into having sex with another or others; in such cases, it may be considered similar to or a form of rape.