Without a doubt my favorite character and quite possibly the reason why I love the show so much. Haruka is a strong and extremely dedicated woman with the heart of a young girl, it's easy to say this because at 29 years old and giving all her dedication to Terra, she somehow manages to re-explore the emotions she once felt as a teenager. I think part of the reason why I love her character so much is because even though she's mature, she's not afraid to show her feelings.
She's a woman of many faces; Haruka is a highly respected captain at Terra, friend of the elite team leader of the Alpha Squadron (Elvy), older sister to Megumi, and hey, ex-girlfriend of Itsuki Kisaragi. Yowzer. And more importantly, she's the face Ixtli decides to take because it knows that she's Ayato's true love.
Haruka is the reason why Ayato got to escape from Terra and indirectly the reason Ayato awoke as an instrumentalist. She depends on Ayato to finish the missions, and so Ayato thinks that she's only using him to pilot the giant robot, because of this Ayato grows distrust for her early in the series, though she later earns it back.
However, Haruka's motives may be a little more complicated than that. Though she depends on Ayato to fullfill his mission, she constantly worries about him and pretty early in the series we're given hints that Haruka has strong feelings for Ayato. This may seem out of the blue at first, but there's definitely a history behind this.
Before Maya took over Tokyo with her Jupiter-like barrier, 14 year old Ayato and Haruka were romantically involved. Not much of this early romance is explored in the TV series, though we do learn this through their stories. When the Mu first started to appear on Earth in their large floating cities and Maya started the process of creating the Tokyo Jupiter barrier, Haruka was away with her pregnant mother visting relatives outside of Tokyo. By the time the TJ barrier finished, Ayato and Haruka were separated for good. However, young Haruka could never forget her first love and eventually comes back during operating Overlord to get Ayato back. Ayato escapes from her several times throughout the series and each time she worries herself sick thinking she lost him yet again.
When Ayato was separated from Haruka for the first time a serious time gap occured. Time flows at a much slower rate inside Tokyo Jupiter, because of this, Ayato aged slowly while Haruka aged normally outside. By the time Ayato was 17 (when we're introduced to the series), Haruka is already 29 and has had a life of her own. During this time, she had studied and graudated from college, dated Itsuki for a while, and eventually moved in with her uncle (Dr. Rikudoh) and started her career with Terra.
It's important to point out that even though Haruka dated Itsuki, she had always loved Ayato. Itsuki on the other hand loved Haruka with all his heart, so the feeelings weren't mutual. There is conflict in this as we see mid-way through the series when Ayato spotted Itsuki forcing himself on Haruka (and thought the two were together for a good while). The drama of it all is that at this point in the series, Ayato was alreadystarting to develop interest in Haruka, so seeing this scene was rather shocking and heart breaking to him. This is why he resorts back to his old friend Asahina for comfort (refer to Asahina's and Itsuki's bio page for more).
When Ayato transforms into the RahXephon (Yolteotl) Haruka becomes desperate to get him back and so she gets on a fighter jet and tries to reach him physically this way. It could be said that at this point in the story Haruka had either completely lost her mind or knew what the consequences of her action would be. In the end though, it worked out. Haruka got to reach Ayato in this 'after-life' after she had a heart-to-heart conversation with Maya, and made Ayato realize what is most important. After the tuning, we can see that she's married to Ayato and has Quon for a daughter. Her appearance in this scene is a bit different from Haruka we knew in the series, as though she's a bit older.
Can't get enough Haruka? Check out her bonus gallery!