In many cases, visual novels are indeed rated by CERO. CERO provides a standardized rating system to determine the suitability of the content for different age groups based on various factors like violence, sexual content, and themes.
I'm not entirely sure specifically what the 'cero essence anime story' is about as it's not a widely known common title. It could be a very niche or self - created anime concept.
In many anime stories, Cero Essence could be acquired through interactions with powerful characters or by uncovering hidden locations. Sometimes, it requires solving complex puzzles or fulfilling certain conditions related to the plot.
Since we know so little about the 'cero essence anime story', it's difficult to say who the main characters might be. However, in most anime, there are characters who are central to the plot because of their relation to the main concept. So in this case, if the 'cero essence' is important, there might be a character who discovers it, or perhaps a character who is born with it. There could also be antagonists who want to use the 'cero essence' for their own malicious purposes.
Well, often it requires the character to overcome significant challenges and develop their abilities. Sometimes it's about making the right choices at crucial moments or having a strong sense of justice and purpose.