Harry Potter and the Order of the Phoenix

Luna first appears in Harry Potter and the Order of the Phoenix when Harry, Ginny, and Neville join her in a compartment on the Hogwarts Express. Luna is isolated at school, but she seems to care little for what others think. She is aware of the nickname everyone calls her—but by which she seems to be unperturbed—"Loony"—by which she is widely known among the students, and is largely unfazed when her classmates tease her by regularly stealing and hiding her possessions. Nevertheless, she values her few friends.

Harry, during this particularly turbulent year of his life, forms a strong friendship with Luna, who is the only person who can quell his anger and calm him down when many of his closer friends cannot, and she supports Harry many times during the series. She and her father, Xenophilius, believe Harry and Albus Dumbledore when they claim that Lord Voldemort has returned; with Hermione, Luna persuades Rita Skeeter to interview Harry so that his views can be published in The Quibbler, the magazine to which Luna's father is the editor. Luna also joins Dumbledore's Army, and later in the book joins Harry, Ron, Hermione, Ginny, and Neville in the conflict with Death Eaters at the Ministry of Magic Department of Mysteries and, when she is separated from Harry along with Ron and Ginny, appears to be the only one uninjured until hit by a stunning spell. Towards the end of the book, Luna consoles Harry by sharing her views on death after the loss of his godfather, Sirius Black.

Harry Potter and the Half-Blood Prince

In Half-Blood Prince, Luna is first seen on the Hogwarts Express. When some other female students invite Harry to join them in their compartment by saying that he does not have to sit with Luna and Neville, implying that they are undesirable companions, Harry witheringly says, "They're friends of mine." Luna observes in her bluntly honest way that people expect someone like Harry to have "cooler friends than us". Harry's response, indicative of the increased fondness he has developed for the pair, is that she and Neville are cool.

At Christmas, Harry invites Luna on a platonic date to the party hosted by Horace Slughorn. Despite wearing a spangled silvery dress, she looks quite nice, Harry notices, and her conversation about the Rotfang conspiracy (where the Aurors are allegedly trying to bring down the Ministry via Dark Magic and gum disease) has Harry coughing into his drink with laughter. Luna also does the Quidditch commentary for Gryffindor's game against Hufflepuff during which she says little about the play – talking instead about "interestingly-shaped clouds" above the stadium and how nice Ginny is and referring to one of the Hufflepuff players as suffering from "Loser's Lurgy". Minerva McGonagall does not quite know what to do with her, but some fans find her commentary highly amusing. This wins over Ron, who remarks that Luna may be mad, but in a good way. Rowling said in an interview that she "really enjoyed" writing Luna's commentary and considered it "blinding insight".^[10][11]

Later, when Death Eaters attack Hogwarts, Luna, Ginny and Neville are the sole D.A. members who answer the call to protect the school. During Dumbledore's funeral, Harry feels a "great rush of affection" for both Luna and Neville as the former helps the latter into his seat.

Harry Potter and the Deathly Hallows

In Deathly Hallows, Luna and her father attend Bill and Fleur's wedding at the Burrow, where she immediately recognises Harry, even though he is disguised with Polyjuice Potion, simply by his facial expression. Luna later returns to school for her sixth year, where she and Ginny help Neville secretly revive Dumbledore's Army, to the fury of Alecto and Amycus Carrow, Death Eater siblings sent to teach at Hogwarts. During the first term, the trio break into the office of Severus Snape and try to steal the sword of Gryffindor to help Harry on his journey. They are captured and apparently punished, but the sanction is a visit to the Forbidden Forest with Rubeus Hagrid.

When Harry visits the Lovegood home, he notices several pieces of evidence that Luna hasn't been home for weeks despite it being Christmas break: dust over a photo of her and her mother, no clothes in her wardrobe, and her bed, which looks like it hasn't been slept in for some time. It is then revealed that while heading home for Christmas on the Hogwarts Express, Luna was kidnapped in an effort to keep her father from publishing information in support of Harry in The Quibbler. When Harry, Ron, and Hermione are at the Lovegood home, Xenophilius, desperate to save his only child, betrays them to the Death Eaters in the hope that doing so will secure Luna's release. The trio narrowly escapes - only to land in the cellar of Malfoy Manor as captives themselves a few months later. There, they find Luna being held hostage along with Mr Ollivander the wand maker. They are all rescued by Dobby the house elf, who brings them to Shell Cottage, the home of Bill Weasley and his wife Fleur Delacour, where protective enchantments keep them safe.

When Harry returns to Hogwarts in search of the Ravenclaw item that Voldemort turned into a Horcrux, Luna helps him enter Ravenclaw's common room in order to view a replica of Rowena Ravenclaw's diadem. She stuns Death Eater Alecto Carrow when they are discovered. Later, she fights bravely in the Battle of Hogwarts and summons her Patronus charm to help fight off hundreds of oncoming Dementors about to attack Harry, Ron and Hermione. After Harry's supposed death, Luna, Hermione and Ginny duel Bellatrix Lestrange, until Molly Weasley takes over and defeats Bellatrix herself. Finally, Luna is among the first to congratulate Harry when Voldemort is defeated. After the battle, she seems to be the only one who sees that Harry needs peace and quiet, so she provides a distraction so that he can escape under his Cloak of Invisibility.