Lydia Kalar is the Queen of Kalar Forest and the mother of Remedia Kalar. She was seduced by Shin and eventually enslaved by him as a devil in his plot of building Blade of Eternality, a blade that can grow inifnitely.
Lydia was the Queen of Kalar Forest and was benevolent to her people as well as the captured human slaves who are usually used to reproduce. She met Shin when he acted as a consultant in a military action against the Kalar Forest in order to claim their crystals. She was seduced by Shin and had an affair with him. The disgraceful affair later got exposed and Shin was sentenced to death. The night before execution, Lydia came to Shin and asked him to flee with the help of the Kalars at her side. Shin rejected the offer and asked Lydia to elope with him. The Innocent Lydia was moved and eloped with Shin out of Kalar Forest. Shin also asked her to have intercourse with him if they successfully leave Kalar Forest.
As promised, Lydia gave her viginity to Shin and later gave birth to their daughter, Remedia Kalar. With the new-joined child, Lydia accompanied Shin in his travel around the world while trying to conceal her status as a Kalar by wearing a mantle.
Lydia met young Hazumi Flamel in her trip and discovered her ability of infinite enchant magic. She took the enchanted dagger from Hazumi and warned her not to use her ability any more.
However, during their travel Lydia is frequently marked as the target for hunting due to her Kalar status. Shin requested her to fight off the robbers, and in the process she killed many of them. Shin also made use of this as a torturing method in his intercourse with Lydia, gradually turing Lydia into a masochist. Under Shin's request, Lydia also caused the rockfall accident at the ancient remain which resulted in grievous injure of Hazumi's father unknowingly.
Eventually, the life of Lydia came to an end and she was to reincarnate inito an angel or devil, based on her deeds as a Kalar. Shin and Remedia witnessed her death and Shin assured Remedia that Lydia is to reincarnate into an angel. Shin and Remedia then went on their trip around the world.
Lydia returned to Shin and Remedia some time after her death, reincarnated, not as an angel, but a devil. It turned out that Shin's demand has added too much sins on her and this made her a demon after reincarnation. Lydia planned to say farewell to Shin and Remedia before starting her job as a devil, but Shin insisted on asking her new name as a devil. Lydia hesitated to tell Shin her new name as knowing the true name of a devil grants one absolute control over the devil. But she eventually gave up and told Shin that her new name is Renli (レンリ).
Upon knowing Lydia's name as a devil, Shin immediately used the power to stop Lydia from leaving. Lydia was astonished at Shin's behavior and Shin revealed all his plot. He has been aiming at all this ever since his visit to Kalar Forest. With absolute dominance over Lydia, Shin ordered her to teleport him to the ancient remains and assist his investigation along, leaving the young Remedia alone with only the sword.
Since then, Lydia has been enslaved by Shin. She acted as his wife in Toushin Toshi and assisted Shin in his building of the most powerful weapon, the Blade of Eternity. It was not until Shin dedicated his own life to the blade did Lydia become free from Shin's mind control. She then assisted Nakuto and Hazumi in their quest for the blade in the devil's world. Along with the help from two other demons, Kurisu (クリス) and Seruji (セルジィ), Nakuto traced the Blade of Eternity and succeeded in dismantling it using the crystal from Remedia.
After the battle, Tero Ettienno, the Eternal Mother of devils, decided that Lydia would continue to pay for her sins as a devil. Lydia confessed her sin and accepted her destiny as a devil.