Perhaps the most complex relationships among characters are the emotional ones because they can grow to any degree in any direction AND because both characters don't have to feel the same way about each other!
For example, how many stories are written about "unrequited love" where one character is infatuated with the other, but the other is repulsed by them, yet in the end both may love each other, both hate each other, or they may have swapped positions, emotionally.
Another example is the younger brother who tags along with the older brother. To the younger, the older brother is his hero. To the older, the younger brother is a pest. Now, suppose the younger brother is attacked by a bully. The older brother may come to the rescue and defend his tag-along. But the moment the threat is gone and the younger brother looks up at his protector with glowing eyes, the older brother say, "Okay, get out of here and leave me alone." Emotional relationships change with the slightest breeze and change back with the least provocation.
Consider the emotional relationships among the characters in your novel or screenplay. Now, consider your plot and also changes in situational relationships, such as who is second in command or married to whom. Go over the emotional journey of each of your characters as individuals. Then, imagine how each emotional relationships might shift, change, and grow for each of the characters due to changes in their situational relationships with others.
It is a fair amount of work, but you will find that this development more than any other will enrich your characters and the passionate experience of your story.
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