Eron Chang is the twin brother to Erika Chang and a descendant of the legendary Dark Ones. He is a few minutes older than Erika. He is an OC introduced in the Arc 1 Prologue and serves as the leading male antagonist in New Trials of Cardcaptor Sakura. However, when he develops feelings for Sakura, he becomes an ally of hers. He is a member of Sakura's Alliance of the Stars.
Eron is the son of Eriko Yoshida and Ryouta Chang. When their mother passed away, he and Erika were taken to the orphanage. At that time, their father had left them. Erika had a weak heart, and was more frail than other children. When they were five years old, she had to make frequent visits to the hospital. By the time they were seven, she had to stay in the hospital for good. At one point, their uncle, Reiji Chang, had taken care of Eron and Erika until he died.
Eron is described to be very good-looking and charming. He has long, dark purple hair that is tied in a ponytail. His eyes are hazel with golden hues in them. He is sometimes mistaken as a girl. He is said to resemble his father, Ryouta. When Sakura first meet him, she describes him as "very charming and good-looking." His smile is described as "brimming with charm and a sense of power." He used to wear a black gem-like rock around his neck, which he wore until he broke free from the Dark One's control. The gem-like rock he wore contained the soul of Ruichi Chang, one of the Original Dark One. He also used to wear a ruby stud earring in his left ear until it was stolen by Kai Mizuki.
Eron is very charming and intelligent. He is also very powerful, shown when he was able to break free of the Dark One's curse after the events of the Plague. He is currently no longer under their control. He is also a perfectionist, shown when he continuously practiced the violin for the Winter Concert. At first, Eron was cold, distrusting, and distant. This was because he and Erika were raised in an orphanage. Though he is cold toward others, he deeply cares for his twin sister Erika. He has a sister complex, shown when he is worried about Erika and her relationships. Unlike Erika, he doesn't have artistic talent.
Eron started to grow soft and caring towards other people, besides Erika, when he started to develop feelings for Sakura. He became an ally of Sakura's and joined the Alliance of the Stars. When Syaoran had left Japan to go to Hong Kong, he started to get closer to Sakura. He began helping her capture cards, such as The Metal.