Anger and focus toward a person or group of people, what is this feeling none other than revenge. Having such intense feeling toward something like getting back at someone, can be one of the many reasons for a characters motivation in a story.
In any decent story, you need to explain where the protagonists drive, aka a plot device, comes from and revenge is one of those explanations; which is quiet prevalent in Shakespeare's work, noted by Zetsuen no Tempest. Speaking of Zetsuen no Tempest, one of characters in it is someone that I wanted to use as an example.
Fuwa Mahiro is a fiery blond that is out to kill the person who killed his sister, Fuwa Aika.
Where the anime is right now, Mahiro hasn't been very forgiving when it comes to screwing over people to find Aika's killer. This is pretty reasonable considering she was killed for no real reason; which at the bare minimum, figuring out who did this and hoping for justice is something that most people would desire.
Despite his burning desire for the blood of his sister's killer, he still can think pretty clearly though his decisions and make a sound resolutions. It is quite a strange personality trait to have with such a high amount of stubbornness.
However, some people aren't as lucky to have a clear head in the heat of battle; after being tormented by Seedless for quite awhile, she distances herself from the friends who are also being targeted by Seedless, there is only one character in Kokoro Connect who comes to mind.
Nagase Iori, the sweet but very self critical president of the Culture Research Club.
After Iori's bitter stages of pushing everyone away from her because she thought no one really understood her, the thing that shook Iori enough was the actions of Setouchi Kaoru and her friends. However, unlike Mahiro, Iori does forgive and actually befriend Kaoru after all the conflict is wrapped up and the CRC was back to normal.
You could say that Iori is the yang to Mahiro's yin in the sense that she was more forgiving, but also not very forward thinking when it came to her response right after finding out about the incident first happened. Regardless, Iori balanced herself out in the end and both Iori and Kaoru are pretty good friends and the past was basically forgive and forget.
Sweet Victory
Even if Zetsuen no Tempest isn't finished, we can quite clearly see both Mahiro and Iori had motivation throughout the story of each anime. They used said motivation in different ways, but revenge is something that can be played with, whether it ends good or bad. These revenge plot can very well have a ton of potential for several series, that shape characters in interesting ways.