The main elements could be the characters' personal growth, their challenges and how they overcome them, and the discovery of true meaning of happiness.
It usually features explicit and sometimes extreme depictions of sexual content with a focus on creating a sense of happiness or pleasure. But keep in mind, this kind of manga is not for everyone and may not be suitable for all audiences.
Achieving personal goals and following her passions is another factor. Maybe it's becoming a great artist or achieving success in her career. Self-fulfillment can definitely lead to happiness. Also, having a sense of belonging and a purpose in life, like being part of a community or fighting for a cause she believes in, can make a woman happy in manga.
The key to fulfilling the wish to grab happiness in the manga might be through self-improvement, building strong relationships, and having a positive attitude. Characters who do these things tend to find happiness along the way.
In the 'secrets of happiness novel', one secret could be strong relationships. Characters who have deep and meaningful connections with others seem to be happier. They support each other through tough times and share joys.