Deai-kei
2=出会い系 means something "for an encounter" in Japanese.
2=出会い喫茶 are coffee shops where men look at girls through a one way mirror and try to start the date if they like the girl. Some coffee shops have been raided because of anti-prostitution laws.
2=出会い系サイト refers to online dating websites. The earliest online dating websites emerged in 1995. NTT Docomo introduced i-Mode in 1999, which allowed users to access the internet through mobile phones. This allowed people to easily access the internet, and contributed to the increase in online dating website users in Japan. These became popular after laws regulating other dating services such as Telephone Clubs were passed in the late 1990s.
Criminal activity
Since the internet gives users anonymity, these websites have been used to commit various crimes including prostitution, false billing and false invoicing, kidnapping, assault and battery, rape, extortion, and murder. As these internet dating websites became a successful business model, the number of service providers has increased. The increased business has resulted in increased reports of criminal activity and has become a social problem in Japan.In the 2011 "Arrest Data on Crimes Involving Dating Websites" report released by the National Police Agency, several crimes including the violation of the Law to Regulate Solicitation through Matching Business via Internet Sites, Child Welfare Act, Provision of Child Pornography and Other Related Activities were listed among other crimes. The number of prosecutions in that year was 1,421. Although 22 of these include crimes such as murder and rape, the vast majority are violations of laws dealing with the child pornography and the welfare of children.