Justice:The virtue of treating others how they deserve to be treated.
In a very personal sense, justice is a defender of your values. If someone treats you poorly, or violate your rights, you should treat them accordingly. You should avoid them, don't trust them, and potentially have them arrested. This is a way of protecting yourself from harm.
The reverse side of justice is making sure those that benefit you are thanked, rewarded, or treated well. You want to make sure that when someone does something for you, they're happy with their choice. In this sense, justice encourages the positive relationships.
Justice doesn't just affect the immediate interactions with the individuals involved. By creating a just environment, it sets the foundation for other kinds of relationships. If you punish those who hurt you, others will avoid it. If you reward those people who have a positive impact in your life, you'll make other people want to deal with you. And in a wider sense, you help create a just world, where positive interactions are the norm and negative interactions are discouraged.