CERO: Z (18+)

Full Name: Computer Entertainment Rating Organization
Country: Japan
Founded: July 2002

From Wikipedia

The Computer Entertainment Rating Organization (特定非営利活動法人コンピュータエンターテインメントレーティング機構, Tokutei Hieiri Katsudō Hōjin Konpyūta Entāteinmento Rētingu Kikō?) (CERO) is the organization that rates video games and Computer software in Japan with levels of rating that informs the customer of the nature of the product and for what age group it is suitable. It was established on July 2002 as a branch of Computer Entertainment Supplier's Association, and became an officially recognized non-profit organization on 2003.

Rating Z (ages 18 and up only) equivalent to ESRB's M and AO ratings, PEGI's 18 (high end) rating, and OFLC's MA15 (high end) and Refused Classification ratings. Games rated Z include Assassin's Creed, Dead Rising, The Godfather, Fable II, Fallout 3, Left 4 Dead 2, MadWorld, Chaos;Head Noah , and God of War III. The content is extreme in the CERO impact levels and therefore off-limits to persons under 18.