Leona (レオナ, Reona), also known under her codename Leona Heidern (レオナ・ハイデルン, Reona Haiderun), is a character introduced in The King of Fighters '96 as the new member to the Ikari Team. Her official nickname is The Silent Soldier (サイレント ソルジャー). 
Before production for her debut game began, developers wanted to create a suitable replacement for Heidern as a part of the game's overhaul. Developers admit that they wanted to introduce the plot element of Heidern's adopted daughter before the production of KOF '96.  Leona was conceived to be an Orochi descendant by the time of her debut and her designers took special care to let their interests at the time reflect in her actions.  Her most recent design was done by Eisuke Ogura, Nobuyuki Kuroki comments on Leona's chest ending up being more robust compared to her previous incarnations. 
In an interview with one of the series designers, Shinkiro, he replies that Leona is his favorite original character in the series. Logo and character designer Nao Q also has Leona as his favourite character, he comments on his soft spot for ice maidens. Garou: Mark of the Wolves planner and The King of Fighters XIV producer Yasuyuki Oda states that Leona and Kyo are his favourite characters in The King of Fighters series. In the Neo Geo Freak's 1997 Volume 8 character poll, she was voted as the fourth favourite character with a total of 1,458 votes. 187 votes from the male fans and 1,271 votes from the female fans. And in Neo Geo Freak's August 1998 issue, she was ranked as the 2nd best character. 
Leona was born in an unnamed village, residing with her family. When she was a child, Goenitz arrived at her home and demanded to talk with Gaidel, the leader of the village. He requested that Gaidel join him in their duties to serve Orochi, as everyone in the village were Orochi bloodline members.
However, Gaidel refused as he and his family liked peace and not the violent tendencies created by the Orochi blood. Enraged, Goenitz leaves; the same night, Leona underwent the Riot of Blood and slaughtered everyone in the village. Goenitz, pleased by the results, puts her blood lust to rest for another time "when he needs her again". Dazed and shocked, she loses her memories and wanders aimlessly until she is found and later adopted by Heidern. Surprised by her natural fighting ability, he decides to raise her as a Ikari warrior under his command.
In 1996, she receives her first official mission to enter the King of Fighters tournament with Ralf and Clark. Their mission was to investigate Geese Howard who had entered the tournament in search of an unknown goal. During the events of the '96 finals, Goenitz confronts her and reminds her of her Orochi lineage, causing her to worry about the future.
Her troubled state carried over to the battlefield, which eventually lead to her and her partners' suspension from military service. Wanting to cheer her up, Ralf enlists them again in the the next year's tournament. She eventually remembers her past fully during the events of King of Fighters '97. Towards the tournament finals, Leona undergoes the Riot of the Blood induced by Orochi. By the tournament's end, she is successfully subdued and Orochi is sealed away. Even so, Leona regrets her actions and attempts to end her life. Ralf stops her, and encourages her to continue living.
Leona stays as a member of Ikari Warriors Team for each and every King of Fighters tournaments during the NESTS saga. It was assumed she partook in her normal duties with Heidern during this time frame.
At the end of the tournament in 2003, Orochi's seal is broken. She enters the Riot of the Blood and attacks Ralf and Clark, badly injuring them. She is pulled out of the team by Heidern in The King of Fighters XI due to the emotional trauma she suffered after the incident. Overcoming the shock, she is designated to join the KOF XIII tournament with her old teammates, determined to live with whatever flaws the Orochi blood invokes. After the tournament's climax, she loses consciousness and sleeps for several days. Her teammates were worried for her and stay beside her until she awakens. Comforted by their concerns, she laughs for the first time in the series.
Leona is a reticent individual who has trouble expressing herself outside of combat or a mission. Due to her past, she often keeps her emotions in check as she is afraid of losing control and hurting her friends because of her Orochi blood.
Aside from Ralf, Whip, Clark and Commander Heidern, Leona does not talk to anyone. She often feels lonely, but is comforted with the new family she has found with the Ikari mercenaries. Ever since the attempted suicide, Leona resolves to take control of her own Orochi blood, using it only when the situation calls for it, something that she tells her opponents in her own pre-fight dialogues.
- Cutting/Piercing Hands - Leona can cut or pierce with her hands.
- Cutting Aura - Leona can create a cutting aura around her hands and feet.
- Cutting Ball - Leona can create a ball of energy surrounded by several energy blades.
- Riot of the Blood - Due to her Orochi heritage, Leona goes into this state whenever Orochi's presence is strong.
- Orochi Power - Leona can exert some control of this state so long as Orochi's power remains weak. While using it, her hair temporarily turns red or shows a tint of red, just like her full-blown Orochi form.
She shares several moves with her adoptive father, Heidern, and she also seems to emulate Ralf's moves. For example; her CD/Blowback attack is almost akin to Ralf's. Also as the games progress, her moves seem to become more explosive much like Ralf's and her style of running changing from being like Heidern's to like Ralf's, but at the same time still maintaining her more agile techniques taught by Heidern; unlike Heidern however, she has more apparent differences in her techniques via extra variations that focus more on speed and acrobatics.
The V-shaped slashmarks that appear at the end of her V-Slasher DM and SDM are an homage to Choudenji Machine Voltes V -- the titular giant robot had an attack in which it made a V-shaped slash through the enemy, leaving a glowing V for a few dramatic moments before it is destroyed.
Her Rebel Spark Desperation Move and Super Desperation Move where she plants an explosive on her opponent then moving away from the opponent while making a pose, is actually a homage to Kamen Rider Black RX -- a Japanese tokusatsu show where the hero impaled his enemy with his sword, Revolcane, and proceed to do the same pose as sparks came out from his opponent's belly and eventually exploded.
Also, her jumping CD/Blowback attack resembles Kamen Rider Black's version of the Rider Kick, owing to the sudden, unexplained glow of reddish energy around her foot, and being performed while in the air. Another sentai homage includes her exploding earrings (Himitsu Sentai Goranger).
Two of her moves are references to JoJo's Bizarre Adventure:
- Her "Earring Bomb 2: Heart Attack" is a nod towards Yoshikage Kira's Stand Killer Queen and its "Bomb #2 - Sheer Heart Attack" ability, as seen in Part 4: Diamond is Unbreakable. She first attaches a bomb to her opponent. Afterwards, she may either wait until it explodes on its own or detonate it with a secondary command, saying 負けて終わり ("Makete owari." ~ "You've lost in the end."), referencing Killer Queen's Bites The Dust ability (transcribed in Japanese as 負けて死ね, "Makete shine." = "You've lost in death").
- Her Grateful Dead (Super) Desperation Move, during which she drains the opponent of his/her life force while surrounded by wisps of steam or smoke, references Prosciutto's Stand The Grateful Dead from Part 5: Vento Aureo, which causes rapid aging in its victim and can differentiate between targets through the body heat they give off.
Her other moves take their namesakes from Grendizer.
- Rumbling on the City - The King of Fighters '96, '98, R-1, R-2, SNK vs. Capcom: The Match of the Millennium
- W.W.III - The King of Fighters '99
- The Trooper - The King of Fighters 2000, EX, EX2
- My Whip - The King of Fighters 2001
- Jungle Bouncer - The King of Fighters 2002
- Inside Skinny - The King of Fighters 2003
- Irregular Mission - The King of Fighters XIII
- Smell of Gunpowder - The King of Fighters XIII (when the music is set to "Type B", console version only, shared with Ralf Jones and Clark Still)
- Survivors Under The Sky - The King of Fighters XIV
- DESERT REQUIEM ~Operation '02UM~ - The King of Fighters 2002 Unlimited Match
- Ray - Days of Memories (Boku to Kanojo to Koto no Koi)
- Rumbling on the City ~SNK Heroines Edit~ - SNK Heroines: Tag Team Frenzy
- Masae Yumi - The King of Fighters '96~XIII
- Seiko Yoshida - The King of Fighters XIV~present
- Lisa Leonard - Maximum Impact series (English voice)
- The King of Fighters '96
- The King of Fighters '97
- The King of Fighters '98
- The King of Fighters R-1
- The King of Fighters R-2
- SNK Gals' Fighters
- SNK vs. Capcom: The Match of the Millennium
- The King of Fighters '99
- The King of Fighters 2000
- The King of Fighters 2001
- The King of Fighters EX
- The King of Fighters 2002
- The King of Fighters EX2
- The King of Fighters Neowave
- KOF: Maximum Impact
- The King of Fighters 2003
- KOF: Maximum Impact 2
- KOF Maximum Impact Regulation A
- The King of Fighters '98: Ultimate Match
- The King of Fighters XII
- Metal Slug XX
- The King of Fighters XIII
- The King of Fighters 2002: Unlimited Match
- CR The King of Fighters
- The King of Fighters XIV
- SNK Heroines: Tag Team Frenzy
- Ikari - Leona Gekitohen
- Days of Memories - (first and seventh games) - Unplayable
- Metal Slug Survivors
- Metal Slug Soldiers
- Metal Slug Team Mission
- The King of Fighters Volleyball
- The King of Reversi
- The King of Fighters Mahjong
- SNK Beach Volley Gal's Attack
- Moeyo! KOF Daiundokai
- SNK Gals Island Dokidoki Puzzle Shock!
- SNK Gals Island Senkan Battle Gekichinshichaouzo!
- Metal Slug Mobile 4
- SNK Gals Island Beauty Dungeon Mimi to Kimashita!
- SNK Dream Battle
- SNK High School Collection
- The King of Fighters '98 Ultimate Match Online
- Metal Slug Defense
- Metal Slug Attack
- Crusaders Quest
- Brave Frontier
- Puzzle & Dragons
- Kimi wa Hero
- HIT : Heroes of Incredible Tales
- Avabel Online
- Mobile Legends - as a Karina skin
- The King of Fighters: Destiny
- The King of Fighters: World
- The King of Fighters: All Star
- The King of Fighters: Orochi Go
- The King of Fighters M《格鬥天王M》
- The King of Fighters XI - Background cameo in Osaka Stage (Only in PS2 port)
- Neo Geo Battle Coliseum - Background cameo
- Garou: Mark of the Wolves - In Hokutomaru's stage during the third round.
- Capcom vs SNK 2 - Background cameo; standing beside Edward Falcon
- The King of Fighters: Battle de Paradise
- The King of Fighters '94: Rebout - Background cameo
- The King of Fighters (pachinko)
- The King of Fighters 2
- Phantasy Star Online 2 - as a costume
- In KOF 98, Leona mysteriously salutes Chang Koehan and belittles Ralf. This was originally thought to be a bug, but developers add that it was her showing respect for "real power". The exact meaning of this statement remains unclear though it became a popular subject in fan doujinshi for a time. They salute one another in KOF XIV.
- In Neo-Geo Freak 1998, the characters in KOF '98 have their own interviews. Here are Leona's response to the questions.
- What is your aspiration in this competition? - "Aspiration...?"
- Who would you like to fight the most? - "Instructor."
- Who would you like to team up with? / Who would you not like to team up with? - "Not selected."
- What is "KOF" for you? - "Mission."
- Finally, please give a word to your fans. - "...Hello."
- In KOF: Maximum Impact 2, Fio compares Leona to Eri.
- The name "Leona" means "lioness" in Spanish. This reinforces the hypothesis that she was born in a Spanish-speaking country, but it is still unknown what is this country.
- ↑ 1.0 1.1 Official site for The King of Fighters XII
- ↑ Official character profile from KOF Maximum Impact Regulation "A"
- ↑ 3.0 3.1 Official character page from KOF anniversary website.
- ↑ THE KING OF FIGHTERS XIV Premium Art Book, p.043
- ↑ KOF 10th anniversary website Shinkiro's interview.
- ↑ KOF 10th anniversary website Nao Q's interview.
- ↑ ArcadeAttack Interview Yasuyuki Oda (SNK) – Interview (30th November 2018)
- ↑ Neo Geo Freak 1997-08 archive Neo Geo Freak character popularity poll results.
- ↑ Neo Geo Freak 1997-08 archive Number of votes from both genders, from Neo Geo Freak character popularity poll.
- ↑ Neo Geo Freak 1998-08 archive Neo Geo Freak 10 best character set original image collection.
- ↑ Neo Geo Freak 1998-08 archive The King of Fighters '98 character interviews.