Diantha appears in Pokémon X and Y as a famous movie star and a notable icon across the Kalos region. She is also a Trainer, but shows more interest in other Trainers who have real potential. She takes a special interest in the player from their first meeting in Café Soleil in Lumiose City and later when she meets the player again in Coumarine City.
"What a strange question... Why would I want to play the same old roles forever? Youth may be beautiful, but it's not all there is to life. Everything changes. I want to live and change like that, too. So I look forward to playing different roles as I get older."
"And who are you two?"
"<player>, right? I heard Lysandre call you that. You both have lovely names. Oh, and you're both Trainers! Don't your Pokémon look happy? I'm a Trainer myself, in my off time. I look forward to us battling someday!"
"Does this make you think of something like Kalos's LegendaryPokémon? Found only here in the Kalos region, right? Nowhere else? Maybe that's not a coincidence."
"Bonds... They really are important to us all, aren't they? When I'm acting, I think I'm always trying to forge a bond between myself and the character I'm playing. If all I think about is how I'm nothing like a character, then I'll just hate playing it. But if I focus on what I have in common with the character and put myself in her shoes, I might be able to understand her. It's the same for people--or Pokémon."
"Oh, never mind me! I'm just babbling about my own things. Let's have a battle the next we meet, shall we? I'm still looking forward to it!"
"Welcome at last, dear Trainer. As you must know, I am the Champion, Diantha. Oh, but you are... You're the child I spoke to in Lumiose City and Coumarine City, aren't you?! Then that means that you are also the one that dear Augustine said... Of course! How could I--?! Oh, I must look like such a fool not to recognize you sooner! You and your Pokémon are the ones who stopped Team Flare for us all! It seems wrong of me to say this, but thank you! You saved us all... I can't wait to see what you and your Pokémon are capable now that I know exactly what it is you've done already!"
"Oh, welcome back! I've been hoping that you would visit again! Battling against you and your Pokémon, all of you brimming with hope for the future... Honestly, it just fills me up with energy I need to keep facing each new day! It does!"
"Witnessing the noble spirits of you and your Pokémon in battle has really touched my heart..."
After being defeated (first time)
"I-I'm so choked up that it's hard to know what I should say, but I...I... I'm just so glad at this moment that I was good enough to be the Champion... After all, it gave me the chance to meet and battle with you and your wonderful Pokémon! Now I understand just why dear Augustine--that's Professor Sycamore to you--said he had to get everything ready for the new Champion! He'll be waiting for us in Lumiose City, but before I take you there... My dear <player>, would you mind coming this way with me?"
After being defeated (rematch)
"That positive hope for the future and the warm feelings that fill your heart... Those things can never be exhausted. They will never run out. Not ever. If you just find a way to share them with others, I know you'll have a happy life. Come along, my dear <player>... You know where we're going next."
"Here we are! I'm so glad to welcome you in. This grand chamber is where you enter the Kalos region's Hall of Fame. This is where Pokémon Trainers will live on forever, remembered always for giving their all in battle to the Pokémon League and for the glory and light that they shared with all. Come, <player>… Your love for your Pokémon… And the way that those Pokémon gave everything they had in battle for you… We'll record them all right here for eternity."
"We will record your experience and the glory that you've shown in facing the Pokémon League here in this grand hall! This will be your--and your Pokémon's--legacy! Come, <player>… Your love for your Pokémon… And the way that those Pokémon gave everything they had in battle for you… We'll record them all right here for eternity."
Café Soleil (post-game)
Before the trade
"Oh, why hello there! That's right... This is where I first met you, isn't it? <player>? You know, I'd really like to learn more about how a strong Trainer like you raises his/her Pokémon. This probably feels a bit sudden, but how would you feel about trading one your Pokémon for my Ralts here?"
No: "No, of course I understand... I'm sure all of your Pokémon are like precious friends to you, right? You can't just give away a friend to someone else that easily!"
Yes: (after selecting the Pokémon to trade) "Heheh. We Trainers all feel a bit nervous when trading Pokémon... but I'm sure it's nothing compared to how the Pokémon must feel!"
After the trade
"Hello, <Pokémon>. I'm glad to meet you. Was it a bit shocking to be traded? I hope you'll come to trust and like me. I promise that I'll take good care of you."
"Oh my! I never thought I would meet you here! Honestly, I didn't! Oh, but--silly me--I should at least do these things right… As Champion and as Grand Duchess of the Battle Chateau, I, Diantha, challenge you."
"Witnessing the noble spirits of you and your Pokémon in battle has really touched my heart..."
After being defeated
(if giving the player an item) "Hehe, here you go! I hope you like it!"
"I just...I just don't know what to say... I can hardly express this feeling... But I'm so glad I got to be Champion and Grand Duchess... Battling you and your Pokémon makes everything seem worth it!"
After defeating the player
"Oh, fantastic! What did you think? My team was pretty cool, right? It's a bit embarrassing to show off, but I love to show their best sides!"
Diantha debuted in The Bonds of Evolution!, where she was shown having an exhibition battle against Magnus. With her Gardevoir, Diantha had very little trouble in defeating her opponent's Absol where it was shown she could direct her Gardevoir through mere eye contact. Ash and his friends later encountered Diantha in disguise, trying to get a piece of chocolate cake from a shop. She agreed to have a battle with Ash, but the battle between Pikachu and Gardevoir was soon interrupted by Team Rocket, who caught Gardevoir and took it away. With the guidance of Diantha's Key Stone, Ash and his friends were able to find Team Rocket. Diantha then Mega Evolved her Gardevoir into Mega Gardevoir, easily breaking out of its confinement and sending the Rocket trio blasting off again.
Just like in the games, Diantha is a famous movie star. She starred in a movie titled "My Sweet, Sweet Lady". She is also a fan of desserts, going out of her way to sample the local delicacies whenever she arrives in a new town. Her manager is Kathi Lee.
In Championing a Research Battle!, Diantha spoke with Olympia about the threat that Kalos was to face in the future, during which Olympia showed her a vision of Zygarde. When Olympia mentioned Ash and his friends, Diantha decided to track them down and let them know what she had heard, eventually meeting them in the middle of a training session. When she was informed about the mystical power of Ash and Greninja, she requested to battle Ash again. Diantha and Gardevoir initially held the upper hand, but as the battle continued Ash and Greninja (which eventually transformed into Ash-Greninja, to Diantha's shock) kept doing better. Diantha eventually decided to get serious and Mega Evolve her Gardevoir. Ash and Greninja, however, managed to perfect their transformation and knocked Gardevoir off its feet. But before the battle could continue, Ash and Greninja both passed out. Team Rocket then tried to get their hands on a weakened Gardevoir, but Diantha easily sent them blasting off again. After thanking Gardevoir for its efforts and making sure Ash and Greninja were okay, Diantha left, but could not help but question the nature of Greninja's transformation and the role Ash and his friends were to play. She also appeared again in another flashback in the following episode.
Gardevoir is Diantha's only known Pokémon. It is able to Mega Evolve into Mega Gardevoir. Gardevoir was first seen fighting against Magnus's Absol, where it used its speed to completely avoid taking any damage before defeating it, doing so without needing to Mega Evolve. Later Gardevoir battled against Pikachu, and was able to complete outmatch its opponent again in terms of speed and power. Before it could win, Gardevoir was captured by Team Rocket who attempted to flee with it. However Diantha followed and Mega Evolved Gardevoir who easily escaped its captors and sent them blasting off.
A younger Diantha in her debut film in Pokémon Adventures
Diantha debuts in the X & Y chapter. She is one of the 17 Successors that have received a Key Stone from Gurkinn. She first appears in Chespin Sows the Seeds of Change, where she arrives at Lysandre Café to shield Y and her friends from Lysandre's Pokémon with her Mega Gardevoir. The two converse on what they think beauty represents, which ends when Lysandre leaves to do other business. After realizing that Diantha is a famous movie star, Y excitedly introduces herself to Diantha. Before they can talk, Y's excitement brings the attention of many of Diantha's fans, who immediately rush in to see her. Diantha later bids farewell to Y and her friends.
Diantha later decides to take a break from acting after her latest movie had come out, much to the shock of her fans and the media. She meets up with Korrina, who had gone into hiding after a brush with Team Flare cost her and Gurkinn the Tower of Mastery. They find Gurkinn being attacked by Team Flare Admin Chalmers and his army of Skrelp and Dragalge. With her Mega Gardevoir, Diantha drives Chalmers away and rescues Gurkinn. The three decide to travel together and find Yveltal's cocoon form before Team Flare, who have already uncovered Xerneas's tree form, does. Further on in their journey, Diantha and the others find a wild Diancie being attacked by a thief. They manage to defeat the thief with their Mega-Evolved Pokémon, but Diancie is forced to find a new home. As it thanks them and leaves, Gurkinn reveals that Diancie is capable of Mega Evolution.
In Tying Trevenant, Diantha's group travels to Route 8, where Team Flare is preparing to take Xerneas's tree by using a group of mind-controlled citizens from Vaniville Town. They find X and his friends captured by Essentia after a failed attempt to rescue their fellow townspeople. While Gurkinn stays behind to rescue X and his friends and Korrina faces Celosia alone, Diantha is ambushed by Malva, who reveals herself as a member of Team Flare and attacks. Malva traps herself and Diantha in a Magic Room, which isolates both of them from the outside world. Malva explains to Diantha that she is simply stalling for time while Team Flare manages to move Xerneas to their base. Although Y and Shauna attempt to break the barrier from the outside, their attempts fail and eventually the Magic Room sinks into the ground.
Team Flare successfully obtains Xerneas, but X and his friends manage to prevent the ultimate weapon from taking any innocent lives by weakening the weapon of most of its power. Despite this and Y having Xerneas join her team, Malva reveals that she defeated Diantha and managed to capture Yveltal, which had been sleeping as a cocoon in the ground underneath Xerneas's tree. Due to Xerneas and Yveltal possessing equal strength, the two sides are forced to have a ceasefire otherwise the battle would lead into an endless war between the two Legendary Pokémon.
In Pinsir Glares, Diantha is revealed to be alive and well, having been hidden underground by Blue, an old acquaintance of hers, to avoid the ultimate weapon's beam. Blue reveals to Diantha that he is searching for "Z", the Legendary Pokémon Zygarde, which has the power to end Xerneas and Yveltal's endless war. Diantha agrees to help Blue search for clues to Zygarde's whereabouts. After meeting with X and his friends on Route 15 and introducing Blue to them, Diantha and Blue head to the Lost Hotel to meet up with Gurkinn again. In Zygarde Appears, Diantha and Blue travel to Anistar City after learning that Zygarde had appeared there. Upon arriving, they find Zygarde in the middle of a battle between X's group and Essentia. Before they can land, Essentia successfully captures Zygarde and escapes.
In Malamar Traps, after learning that Team Flare went into hiding at Pokémon Village, Diantha, Blue, and X's group all head out to confront the villains. On the way to the village, the group is attacked by Xerosic, who uses his Malamar to put everyone to sleep. In Yveltal Steals, Diantha is revealed to have woken up and goes on ahead to the village while X and Blue stay behind to fight Xerosic. On her way, Diantha is intercepted by Malva, who used her Talonflame to attack her. By utilizing a technique used by another Trainer in the past, Diantha blocks Malva's attack, only to find that Malva managed to snatch her Mega Charm away.
When Malva escapes by taking to the skies, Diantha follows after by having Gardevoir move them through the air. The chase takes them to the skies above the Pokémon Village. When Y sees the two fighting, she helps Diantha by having Fletchy burn Malva's hand to force her to drop the Mega Charm. Y attempts to assist with battling Malva, but Diantha refuses and asks her to stay out of the battle. After some time, Malva witnesses Lysandre's defeat as the Zygarde he was controlling begins to separate from underneath his feet. This distraction allows Gardevoir to get a hit on Talonflame, which causes it to drop Malva. Diantha attempts to help Malva by reaching out with her hand, but Malva rejects her and ends up falling onto the rubble after failing to catch Lysandre. After Team Flare is fully defeated, Diantha and the remaining Elite Four members carry Malva's unconscious body away.
Diantha was introduced as a Supporter card in the Pokémon Trading Card Game during the English Sun & Moon Series (the Japanese SM Era). It was first released in the Japanese Forbidden Light expansion expansion before debuting in English in the Forbidden Light expansion, with an illustration based on the Ken Sugimori artwork of the character. It was also released as a Full Art card in Forbidden Light with an illustration by nagimiso. It allows the player to put 2 cards from the discard pile into their hand if one of the player's Pokémon was Knocked out in the opponent's last turn.
Diantha is the only Champion to not use more than one Pokémon of the same color. Furthermore, each of her six party members has a different stat as their highest stat. Her team is as follows: Hawlucha (Green, Speed); Tyrantrum (Red, Attack); Aurorus (Blue, HP); Gourgeist (Brown, Defense); Goodra (Purple, Special Defense); Gardevoir (White, Special Attack).