One of the most defining legal aspects of Japanese adult media is censorship. Article 175 of the Japanese Penal Code forbids the distribution of "obscene" materials.
Do not read the synopsis. Just watch the first 90-minute episode. What appears to be a cute idol anime pivots into a dark, psychological revenge thriller about the dark underbelly of the Japanese entertainment industry. It dethroned Fullmetal Alchemist as the highest-rated manga on MyAnimeList for a reason.