Claire - Her older sister apparently went mad and stole Leavantain and caused the Fire Elemental Lord to steal fire from Ordesia, leading to the Elsteins losing everything and Claires parents being imprisoned. Before Kamito came, she had no friends aside from Rinslet (who she pushed away) and her classmates constant torment led to her becoming the firey-tempered Hell Cat she is today.
Rinslet - Her younger sister was frozen by the Water Elemental, and she had to watch her best friend slowly lose herself in power-lust before Kamito came
Ellis - Her older sister (sensing a pattern yet?) was driven insane because of her loss to Ren Ashbell, and she was being pressured to live up to ridiculous expectations as the Knight Captain
Fianna - Traumatized by Rubia, she lost her spirit and was disowned by her family.
And last and greatest, Kamito - Raised as an emotionless weapon, he regained his emotions through Restia... who was then taken and sealed by the Institute. After saving her, he was forced to work for Greyworth to unseal Restia. After accomplishing that, he joined the Blade Dance to accomplish Restias wish...and lost her in doing so. He spent the next three years wandering helplessly trying to find her.
To a certain extent, Rubia. Her every hope is systematically crushed no matter what she does.
As the Fire Queen she was unable to protect those under her charge.
The Fire Elemental Lord demanded Claires life and would not budge, not even when Rubia offered her own in exchange.
Confronting the Elemental Lords in desperation, she learns they've been corrupted and are leading the world to destruction.
She fell into despair and was willing to give up everything, including her sister Claire in order to prevent the world from being destroyed.
Against all odds, she succeeds and awakens Kamito as the Demon King and Claire as his Queen. However, Claire breaks her control and refuses to obey her plan, instead saving Kamito and calming his rage.
She then attacks Kamito with everything she has left, trying to force him to re-awaken. However, Kamito calls back both Est and Restia, and crushes Rubia in seconds, severing her contract and leaving her powerless.
Speaking of Rubia, the worst of it was revealed after: Her plan never could have succeeded in the first place. The Demon King was corrupted by the same thing as the Elemental Lords, meaning she was jumping from the frying pan into the fire. As Sjora Kahn said, she was a truly pitiful existence.