What does the Japanese horror film Curse mean? Why don't I understand? Who is the hero? Please elaborate!

General plot: Chuanyoujia Coconut was withdrawn from childhood and was not close to people. But he has a favorite person, Shunsuke Kobayashi, so she recorded everything Shunsuke said and did. However, Kobayashi Shunsuke married Nami, so Kayako decided to break up the relationship. She married Xiong Gang in Saeki and gave birth to Takashi Saeki Kaya. Saeki Xiong Gang wanted a daughter, but Kayako couldn't get pregnant, so they went to the hospital for examination and found that it was Xiong Gang's oligozoospermia. So Saeki Xiong Gang killed Kayako, threw her body into a plastic bag and put it in the attic. Fearing that his father would hurt himself, Takashi Saeki Kaya hid in the attic, found his mother and was taken away by her. Saeki Xiong Gang is not Japanese, so he rushed into Kobayashi Shunsuke's house and killed Nami and the baby in his belly. At this point, Kobayashi Shunsuke went to Saeki's house and was killed by Kayako. They became enemies. Saeki Xiong Gang was on his way, too, and was killed by Kayako.

The above is the origin of the story. What happened later was that a man was killed by Kayako.