Four years ago Claire's older sister, Rubia, seemingly went mad and stole a powerful fire spirit, which caused the Fire Elemental Lord to steal fire from Ordesia, and rain an inferno upon her family's territory. As punishment for their daughter's betrayal the Elsteins, previously one of the most prominent noble houses in the empire, were stripped of everything and imprisoned, leaving a young Claire without her parents or her older sister. Before Kamito came, she had no friends aside from Rinslet (whom she pushed away) and her classmates' constant bullying led to her becoming the firey-tempered Hell Cat she is today.
After spending three years searching for her, yearning to be with her once again, Kamito is rendered immobile when Restia finally appears before him. However, their reunion is a brief one, as she claims responsibility for the recent incidents, and let's a spirit run rampant, endangering many innocent people. As Restia leaves after promising to meet again, Kamito sinks into despair, convinced that it is his fault Restia became such a cruel person.
Volume 2
Claire wasn't the only person affected by Rubia's actions four years ago. Fianna, Ordesia's second princess and the Fire Queen candidate meant to replace Rubia in case anything happened also went through a great deal of suffering following the events of that day. Rubia was Fianna's senior and friend in the Divine Ritual Institute, so when she was in the process of stealing Laevateinn, Fianna felt it was her duty to stop her, or at least slow her down a little. However Georgios, her spirit, was immediately defeated and Rubia left unimpeded, after telling Fianna never to appear before her again. Her confidence shaken, and having been traumatized by her adored senior, Fianna loses her connection with her contracted spirit, and the ability to commune with spirits in general.
This leaves her unable to assume Rubia's position as Fire Queen, and thus powerless to try to appease the Fire Elemental Lord's fury. As a result, Fianna is disinherited by the royal family, and subjected to the scorn of those who had previously praised her as a prodigy. She spent most of her time afterwards in the palace, with no purpose and no hope. Not until she met Kamito.
Claire's prideful personality crumbles momentarily as she begs Kamito, who had just been asked to join Ellis' team, not to abandon her. Her abandonment issues run deeper than she would like to admit.
Volume 3
Velsaria used to be Ellis' example on how to be an exemplary knight, but she changed for the worse following her defeat at Ren Ashbell's hands during the previous Blade Dance. She became cold and ruthless, seeing no issue with using her overwhelming power to trample her fellow students underfoot in her previous role as captain of the Sylphid Knights. Ellis' attempts to live up to the knightly standards her sister used to embody are met with nothing but disdain by the person in question, who became convinced power was the only thing that mattered.
Ellis faces her worst moments in this volume. Trust on the Sylphid Knights is at an all-time low due to their failures to stop Jio Inzagi, making Ellis feel insecure about whether she is a proper knight at all. Not helping matters is the fact her friends and comrades Rakka and Reishia are hospitalized, leaving Ellis feeling isolated. As Kamito notes, she is under a lot of pressure, far more than any girl should have to endure at such a young age, and with no-one to confide in. Following an incident in which she is once again humiliated by her sister, she locks herself inside her room in tears, convinced of her own failure as a knight.
Kamito's bonding with the Sylphid Knights and specially Ellis causes Claire's jealousy to reach new heights, going as far as kicking him out of the room for daring to “wag his tail” at the Sylphid Knights, with whom she has a bad relationship. She regrets it almost immediately, but Kamito doesn't come back that night, much to her dismay. Further attempts at making up with him are thwarted by her own pride and stubbornness. The worst part is that she realizes Kamito has no ulterior motives for working with the Sylphid Knights, and that he is just trying to help them; yet she can't help but resent the fact that she is not the only person that is special to him.
Volume 4
Kamito had been striving to keep his past as an orphan from the Instructional School hidden, fearing he would be loathed or pitied by the other members of Team Scarlet. So following repeated attempts by Claire to ask him about his past and about Restia, coupled with the recent encounter with Muir unearthing some unpleasant memories, Kamito finally has enough, and rudely tells Claire to stay out of his business. Dejectedly, Claire leaves him alone, and Kamito soon regrets the way he talked to her. Later, Claire is witness to the scene of Kamito and Restia kissing, which leaves her in tears. Even though she recovers enough to attend the ball party later that night, the memory of what she saw, plus the pushy attitude of a prince trying to force her to spend time with him causes her to run out of the ballroom alone.
Muir was an elementalist born from commoners, so she was considered a miracle child by everyone in her village. They tried to have her commune with their village's guarding spirit in order to bring about prosperity to them. However, Muir's innate talent of Jester's Vice instead resulted in said spirit losing control and going on a rampage. Muir ended up ostracized by her village as a cursed child after this, and it wasn't long before the Instructional School picked her up, and turned her into a merciless killing machine.
Muir's dangerous obsession with Kamito stems from the fact that when they first met, Kamito saw she was always alone, so he promised he would be her older brother. This small kindness is enough for her to desperately cling to him, despite Kamito himself no longer remembering it.
Others
Fianna - Traumatized by Rubia, she lost her spirit and was disowned by her family. In Volume 14, Fianna becomes the victim of a conspiracy led by her own brother Arneus, in order for her to be framed for the death of the Prime Minister and him to access the throne. She is imprisoned, tortured and undernourished to such a degree where the bond with her spirit is almost severed. She was going to be executed until her friends saved her just in time.
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
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 Restia's 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.
