In addition to being Adroc's and Blau's daughter and Renton's older sister, she is also the niece of Yucatan Iglasias, the sister-in-law of Eureka, the paternal aunt of Amber Thurston and Ao Fukai, and the adoptive paternal aunt of Maurice, Maeter and Linck.
Diane has brownish-red hair and blue eyes. She wears a blue dress with white pants, and is average in height.
Diane is an intelligent, mature and kind woman who is best known for her close relationship to her brother, Renton, and her previous romantic relationship with Holland. After their mother died during Renton's birth, Diane took over the role of a surrogate mother figure to him, and this made her more responsible for him when their father disappeared and was later declared dead. Despite this sudden responsibility at her young age, Diane was a loving older sister to Renton and taught him to believe in himself if he wanted to accomplish what was important to him. Like her father, she was interested in science and research of the Scub Coral, leading her to follow in Adroc's footsteps as a scientist and, subsequently, disappear. But before leaving home for good, she left Renton with their grandfather in order to make sure he would be taken care of and reminded him to always believe in her if he wanted to see her again. Because of this, Renton credits his sister for shaping him into someone who believes in accomplishing the impossible.
Before Renton was born, Diane was doted on by her father, Adroc, and able to roam freely at the military base he worked at. When she was about ten-years-old, it was at the same hill Renton would later lift at in Bellforest that she first met Holland, who was then 14-years-old and attempting to lift. She immediately took an interest in him and kissed his forehead to express her feelings, but he initially rejected her. After this, they didn't meet each other for more than five years. After her mother died giving birth to Renton, Diane became a surrogate mother figure to him and she was very close with her father, and she was left feeling sad and confused after his disappearance when she was 16. In her grief, she reunited with Holland and they began a romantic relationship, against Axel's protests; in fact, their first date was almost ruined when a 5-year-old Renton hid her shoes. From Holland's account, their relationship was intitally a happy one until Diane became obsessed with her father's work and was determined to finish what Adroc started. This led to her breaking up with Holland who was adamant that communicating with the Scub Coral was pointless and asked her if she was willing to die for her father's research. After that conversation, she cut off all communications with Holland and left Renton in the care of their grandfather, never to been seen or heard from her family ever again. As the years passed, many people suspected that she was dead and Axel himself considered the possibility, but Renton refused to believe it and maintained his belief that he would see her again. Despite appearing in Axel's family photos and in a silhouette in the series opening, her face isn't shown for the first 35 episodes — under many different circumstances, her face in flashbacks and photographs is always covered, or in Holland's case, scribbled over.
Despite her absence, her presence continues to have a profound effect on those close to her, particularly Renton and Holland. The sudden breakup and her disappearance left Holland bitter and obsessed with her, and unwilling to let go of his feelings for her without knowing her fate. Talho is troubled by Holland's past relationship with her, and reacts with anxiety at her mention. Holland's troubled feelings towards Diane contribute to his abusive attitude towards Renton; he saw the boy as a reminder of his first love who dumped him. Renton keeps the memory of his sister close to him throughout the series; frequently asking her in his mind about the events around him and what his purpose in life is. Much of the first few episodes' narrations are made as if Renton was writing letters to his sister. Her last words to him before she left were for him to always believe in himself so that they can meet again, and because of this, Renton becomes someone who is willing to try to overcome the impossible, no matter how slim his chances are.
In episode 47, Renton discovers that Diane somehow ended up in the Command Center of the Scub Coral. There, in a library artificially created by the Scub Coral, she and a small group of people read to understand the truth they seek. The vast knowledge they wish to seek would take almost a lifetime and all that remain are there under their own volition. She explains the history of the Scub Coral and the consequences of the Limit of Questions if the Command Cluster were to be destroyed. Renton, along with Eureka and the kids, leave the Command Center to initially protect it, but this fails after Anemone succeeds in planting a tracker onto the Command Center. This allows Dewey to pinpoint it's location and destroy it with Oratorio Number 8. Even though Diane told Renton they'll stay together, the Command Center ended up being destroyed anyways. In the final episode, after Renton goes in and saves Eureka from within the orb that the coral begins creating to replace the previous Command Center, the Nirvash pushes both Renton and Eureka from the coral and becomes the new Command Center, as well as taking half of the Scubs with it to another universe. It is unknown if Adroc and Diane are still inside, continuing their research.
- Diane's hairstyle is very similar to her adoptive niece's.
- Diane and her adoptive niece also share the same english voice actress, Peggy O'Neal.
- Diane's fate is never revealed in the manga; it is believed that she is likely dead, but otherwise, what happened to her is never explained.
- Also in the manga, she plays a minor role compared to the anime series.
- Her attire is identical to the one her sister-in-law, Eureka, wears in Eureka Seven: AO.
- Her close relationship with Renton is similar to the closeness between Eureka and Ao in AO. Renton and his son, Ao, were children when Diane and Eureka disappeared, both received important gifts from them (Renton got his Compac Drive from Diane and Ao received Eureka's bracelet, both used to awaken their respective Nirvashs), and both continue to be haunted by their presences (Renton would reunite with Diane at age 14 and Ao would reunite with Eureka at age 13).