The girl was angry at her father for leaving her and her mother alone at home, always working and never being with them. The father's coworker (bloody man) also worked all day, but he had no family waiting for him. He was jealous of the father, so he wanted to take away his family. He killed the mom and daughter out of jealousy.
The ghost of the little girl went into a rage, and blamed the videogame for taking her dad away, her mom away, and her own life away. She killed everyone related to the game, including the other programmers (which you saw in the statues) and anybody who played it... (the girl and guy from the college, who also became statues)...
She also turns you into a statue, if she catches you!
She blames the game, so she kills anyone who is remotely connected to it. In the end, her mother appears to tell her that she doesn't want her to hate her father... And basically the dad comes to you and says that he made the game for her... You see that the name of the game is Load to Sunrise... "Sunrise" is the English translation of "Asashi" (the girl's name).
The main character asks how the game is supposed to end, and then you see the credits which show scenes from the family's life... Marriage, having a baby, etc.
In the "perfect" ending, you get an e-mail on the TS (twin screen, which is like the Dual Screen). Asashi sends you a message "Thank you."
This is one of only two differences between the normal and perfect endings. The normal ending has 8 bit music playing during the credits. The perfect ending has a big symphonic version. To get the perfect ending, you have to find all of the "hidden items" in the 8 bit game which can be found by examining certain objects.