The Realism of Code Geass

[Spoiler alert! go watch it!]
Code Geass is about a high school aged kid with hypnotic powers taking over the world with mechs. It may be a bit hard to see how that is realistic at first, but sifting through the Code Geass timeline gives examples of grounded and realistic scenarios. The most realistic part of the story is its characterization of the hero, Lelouch, and how his conviction to be the revolutionary Zero wavers throughout the series.

I'll give you some background here because the code geass Wiki page is the most efficient way to destroy your eyesight. Lelouch's enemy throughout the entire two seasons is the Britannian Empire, lead by Lelouch's father, Charles. Normally, this would make Lelouch a prince, but after complaining about the assassination of his mother, he was exiled to Japan, under protection of the Kururugi house. Lelouch became friends with Suzaku Kururugi before Japan was invaded by Britannia. The most important people to Lelouch's development are Nunnally (former Britannian princess), Suzaku, Euphemia (current Britannian princess), Shirley (Lelouch's classmate after the invasion), and Kallen (Lelouch's ace pilot).

yes, there are that many characters

Lelouch starts his adventure witnessing a truck crash. He looks around and sees everyone staring, taking pictures, and wondering who would help out. This scene alone is enough to establish Code Geass as being an important commentary on the real lives of its viewers, but it goes beyond this. Lelouch remarks that no one is willing to help, so he decides that he, personally, would be the only one to do so, all while the crowd mocks him for it. He ends up stuck in the truck while its driver pulls into an abandoned subway system and soon after is given his hypnosis power, called "Geass."

The first person to cause turmoil within Lelouch is his school friend, Shirley (who is attracted to him). They got along great until Lelouch's revolutionary army kills Shirley's father. This makes him question whether what he is doing is truly right. Such a dilemma always exists when soldiers face the consequences of their fighting, and Lelouch is hit hard by the knowledge he is causing his friends to suffer. It is only after he concludes that he started his mission knowing that there would be casualties, does he put the issue behind him and continue the fight.

Around that time, Suzaku transfers into Lelouch's school and they start discussing whether Zero's methods are correct or not. Suzaku becomes acquainted with Euphemia who wants to create a specialized sector of Japan where the Japanese could live independent of the laws passed by Britannia. This is the moment that puts Lelouch to the test, as he wants a full scale revolution, but cannot make an argument against Euphemia's plan, nor can he bring himself to fight her, so he admits defeat. They have a secret one-on-one meeting where Lelouch tells her about his geass power. While trying to explain it to her, he accidentally uses it to order her to kill the Japanese people who had gathered in favor of her plan. He is able to retain the public image as Zero at the cost of the lives of thousands of Japanese, and his completely innocent sister. He is forced to put his emotions aside and spin the tragedy in his favor, when all he intended was to work together with Euphemia. His reaction to the event is the most realistic emotional reaction I've seen in an action anime. He loved her almost as much as Nunnally, so having to kill her to save face sticks with him throughout the entire second season, knawing at his conviction, and leading him to question his own morality.

Poor Euphie; she just want to help.

At the beginning of season 2, Kallen knows Zero's identity and power, so she starts to doubt him, wondering if her participation in the revolution really comes from her own will, or if she was manipulated with the geass. Known only to the veiwers, Lelouch only ever used it to ask her questions. Kallen slowly falls in love with Lelouch over the course of the story. Kallen's arc combines with Nunnally's arc a bit because in season 2, Nunnally is made the viceroy of Japan. She tries to reestablish the independent Japanese government Euphemia had tried before, and its impact on Lelouch is even more severe. Lelouch had previously vowed to never go against Nunnally, and he didn't want to repeat the tragedy Euphemia went through, so he became depressed. To continue the fight would have made him go against his principle never to work against Nunnally, so he found the only out he could: giving up. The only shows I've seen with a character go through a realistic depression are Code Geass, and funnily enough, Charlotte. He went around town willy-nilly, using his power to poke fun at random strangers and taking drugs. Kallen steps in to re-inspire him, giving him an out he hadn't considered before. To Kallen, this deepened their connection, but Lelouch still only saw it as a soldier doing what she should. Lelouch acts against Nunnally again at the end of the second season, stealing the Key of Damocles from her but by then he had steeled his heart, having prepared for any sacrifice necessary.

Shirley makes a return in the second season, acting much more loving than she did in the first. One of the slice of life/comedy episodes was dedicated to a school competition to see who would become a couple. Lelouch and Shirley were declared the couple, and they shared a romantic moment. The episode after, Shirley regains her memories and goes to make Suzaku reconcile with Lelouch. However, she is caught by Rolo (a fake brother turned real friend to Lelouch) who recognizes the threat caused by her recovered memories, and kills her. The emotional turmoil that Lelouch experiences leads him to the first thing anyone would think of: revenge against Rolo. He spends much of his time after then trying to kill Rolo unsuccessfully. When Rolo ends up saving his life later, he feels guilty and confesses all he intended to do. This was a very human moment for Lelouch, as he drops his strong, calculating persona to have an honest conversation with Rolo after all the tragedy and all the lying.

Surely not Shirley.