THE CURSEThe "curse" of the Sohma family is the blood-bond between God and the members of the zodiac. Although there are only twelve zodiacs, thirteen people of the Sohma family are effected. This is because there is also a spirit of the cat, which is the most hated of them all. Those who are possessed by the spirit of each of these animals were born two months premature, and have a curse that follows them. If they are hugged by a person of the opposite sex, or they are under great stress, they will transform into their animal form. However, this rule is disregarded if they are both members of the zodiac. An example is when Kagura hugs Kyou constantly, this is because she is able to touch him without any worry of transforming. Once again, this blood-bond allows them to be together, forever. Another thing that will happen during the curse is that each animal will be attracted to their human form. For example, we see Kyou covered in cats because they sense him having the cat-spirit within him. When the Zodiac see "God" for the first time, for an unknown reason, they all start to cry. This reassures Akito that their bond will never be broken.
Akito herself makes this curse even worse, because of her insecurities. She doesn't allow any of the members to fall in love with anyone else, because they all belong to her. One example of this is when she cuts Hatori's eye open when he confesses to her about falling in love with Kana Sohma. Not only that, but Akito screams and blames the Kana for his misery, not herself. This ruins the love for Hatori, and ultimately leads in him removing Kana's memories of them. Besides for romance, Akito is also mentally abusive. She locks Yuki up in a room as a child to sit alone and suffer. She gets great joy out of this, and psychologically damages Yuki for a long time. I believe that if Akito was a lot nicer to the zodiac members, the curse wouldn't really be as bad as it seems. However, the emotional, physically, and mental abuse that she caused all of the members was a curse in its own.
We find out that the curse can be uplifted if the circumstances are right. Kureno is the first one that was able to break free from the curse. He didn't know how it happened, it just did. He proves this to Tohru by holding her close, showing that he no longer can transform. The only true way that the curse can be uplifted for everyone is if God sets the cat zodiac free. When all of the zodiac members are set free in the end of the series, because Akito frees Kyou from his fate, they all feel a bit of sadness. It became lonely without the blood-bond. This is because they all believed in the curse for so long, that being set free from it was almost unrealistic. To have their freedom also meant to fear that they could potentially be all alone. This was scary, but it was something they all were willing to take chances with.