Sieg Hart is a powerful magician/elementalist and his purpose is to preserve time flow. He want to destroy Elie because of her Etherion's power that threaten time.
In the Rave Master franchise, no current information on ideas on the inspiration. However, the author mention he is a fan service by basing Jellal's appearance off of Sieg Hart for his Rave Master fans. (In Fairy Tail volumes)
Before the Mystery of Elie Arc, Sieg Hart is focus on killing Elie to protect time, and he tries to force Haru to pick between saving the world or saving Elie. He is surprised by Haru's quick decision when Haru saves both. This causes Sieg Hart to think and to believe in the Rave. (Will fill in with more info is found)
Sieg Hart appears in Elie's flashbacks. He attacks Elie with lightning without reason.
He appears before King with his Oracion Seis members, Reina and Jegan. King orders Sieg Hart to attack the Rave Master. Outside the meeting, Reina asks what will Sieg Hart do when he meets the girl, he replies that he will kill her. After Elie gazes at Resha's portrait and tries to remember her flashback, Sieg Hart and Reina are on top of a building sharing a conversation about Elie and her powers. Sieg Hart explains to Reina that Elie's power, Etherion, can cause more damage than Overdrive. When he tell Reina that he will do anything necessary to save time if it means killing Elie and King, he provokes Reina in challenging him. As Sieg Hart prepares to fight Reina, he hears Elie's scream. He leaves Reina to go after Elie.
When Sieg Hart finds Elie, she is crying. Elie, who recognizes Sieg Hart due to Go's photo, asks Sieg Hart if he knows her. First, Sieg Hart introduces himself as a protector of time and his most dangerous enemy is Etherion. He explains that Resha is the first user of Etherion, but after her death, people continue to experiment on Etherion. Sieg Hart tells Elie about a lab he found a year ago that he destroyed. In the destruction, he tells Elie that the survivor had the numbers 3173 on her arm which is Elie. At first, Elie tries to deny Sieg Hart's accusation, yet he shoots lightning at Elie's arm which reveals the same digits. Elie grabs Sieg Hart and begs him to tell more about her past because she believes she has a family. As he place his hand on Elie, he reassures her that she will die painlessly for a good cause. When Elie backs away, Sieg Hart attempts to kill her with lightning first.
Elie is on the ground with her body shaking violently from Sieg Hart's attack. When he sees Elie is still alive, he shocks her more violently. During his attempts on taking Elie's life, he explains that Etherion has the power to create when Resha uses to create the Rave. On the other hand, Etherion has the power to destroy as well. After realizing the lightning element is not working effectively, Sieg Hart decides to use the poison element on Elie. He first opens Elie's mouth and shoots poison with his fingers. At the last moment with Elie's life flashing before eyes, Sieg Hart summons another lightning attack, but at the nick of time, Haru takes the blast with his sword.
Even though Sieg Hart does not desire to fight Haru, Haru, who has finish whispering his promise to Elie, swears that he will avenge Elie. Haru lands the first attack, Explosion, on Sieg, but Sieg stops Haru's attacks with his fingers. When Haru uses Siphalion, Sieg uses the wind to move Haru back to evade his attacks. Haru asks Sieg Hart about his Dark Bring; he replies that he has no Dark Bring but his magic. Sieg Hart states that magicians will always defeat swordsmen. Sieg uses the poison element in a form of a cloud that surrounds Elie and Haru. Suddenly, Haru cuts the poisonous cloud with Rune Save. Before Sieg Hart responds, Haru uses Explosion to create a cloud. Sieg Hart waits for Haru's attack, but Haru surprises him with an attack by his regular sword, Eisenmeteor. Sieg Hart learns that objects that have no magic are immune to magic. He rises in the air to evade Haru and attack Haru with flame magic. Sieg Hart warns Haru that Elie's magic will run wild, and he asks Haru whether he will save the world or Elie. When he hears that Haru will save both the world and Elie, Sieg Hart decides to use Altairis on Haru.
As he have Haru trapped in Altairis, Reina appears to give Sieg Hart a good job, but she stabs him in the back with a knife. Then Reina gets caught from behind when Musica uses his silver whip. Sieg Hart realizes Elie is gone, yet Reina, who purposely kept her lips shut, informs him that Elie has gone inside Altairis.
Sieg Hart is a powerful magician who has control of the elements.