Born in Tokyo, Hayashibara was part of the wave of voice actors, particularly actresses, such as Hekiru Shiina and Mariko Kouda, that were marketed to celebrity status during The '90s due to the large amounts of money provided by recording companies, and the more multi-media approach to stardom developed at that time.
Debuted while double majoring in voice-acting training school and medical school as a kindergartener from Maison Ikkoku, she received her first official gig and Star-Making Role as Himiko Shinobibe of Mashin Hero Wataru; which led to her stardom as girl-form Ranma of Ranma ½ shortly after.
As of current, she stands as one of the most legendary of Japanese voice actresses in the business due to her extreme talent and resume. Just by naming any of the roles listed below alone would be a career-making milestone for a voice actress, but as a Woman of a Thousand Voices, Hayashibara has the talent and skill to win that kind of part again and again. She is such a major figure in the anime industry, that the character of Megumi Reinard in Martian Successor Nadesico was actually based on her; partly as parody and partly as tribute. She is arguably one of the few voice actresses who isn't set in a role. Her huge number of voice credits have invited comparison to Mel Blanc, June Foray, and Frank Welker in American Animation.
Whenever she takes part in an anime project, she would frequently take on the case to perform its theme song, most notably for the Slayers series, Saber Marionette J, and Shaman King. She was also noted to take part in "voice actress idol groups," such as DoCo for promoting Ranma ½. Her accomplishment in breaking into mainstream J-pop as a voice actress paved the successful singing careers for the generation of voice actresses after her, namely Nana Mizuki, Yukari Tamura, and Yui Horie.
She's also known to dub American animations, most notably as Batgirl/Barbara Gordon in Batman: The Animated Series, Diddy Kong in the Donkey Kong Country TV series, Sam Manson in Danny Phantom, Crysta in FernGully and Little Sneezer from Tiny Toon Adventures.
She authored (but didn't draw) a biographic manga about her experiences as a voice actress, titled Megumi-Toon.
As she slowed down her pace to focus on her family, she would continue to take on her long running roles for steady income, and own her own personal management agency to take cases only when a project request her for a role.
Just to name a few of the characters she's voiced, she has been:
- Achika in Tenchi Muyo in Love
- Ai in Video Girl Ai
- Ai Haibara from Case Closed
- Aki Kisaragi in Tekkaman Blade
- All female voices for the Japan Animator Expo (at least for the shorts that contain voice work)
- Anna Kyouyama in Shaman King
- Arioch in Drakengard
- Dr. Avery Ryan (Patricia Arquette) in the Japanese dub of CSI: Cyber (replacing Rica Matsumoto)
- Bakabon in Heisei Tensai Bakabon
- Blanc Neige in Shining Tears (though replaced by Ayako Kawasumi in Shining Tears X Wind)
- Blind boy who meets Majin Buu in Dragon Ball Z (Darrin'd by Houko Kuwashima in Dragon Ball Z Kai)
- Canal in Lost Universe
- Casey Becker (Drew Barrymore) in the Japanese dub of Scream (And just like Barrymore, she also invoked Dead Star Walking in that dub)
- Christina MacKenzie in Gundam 0080
- Christine Gillum in Expelled from Paradise
- Chuck in the Japanese dub of Help! I'm a Fish
- Dana Tasker in the Japanese dub of True Lies
- Diddy Kong in the Japanese dub of the Donkey Kong Country cartoon.
- Due Flabellum in Project X Zone
- Elle Ragu in Shadow Skill
- Esmeralda/Satanico Pandemonium (Ara Celi) in the Japanese dub of From Dusk Till Dawn 3: The Hangman's Daughter (very brutally Playing Against Type)
- Falzeb in Zettai Muteki Raijin-Oh, Super Robot Wars GC and Super Robot Wars NEO
- Faye Valentine in Cowboy Bebop
- Freyja in Fire Emblem Heroes
- Young Genkai in YuYu Hakusho
- Hakumen no Mono in Ushio and Tora
- Haruka Urashima in Love Hina
- Hello Kitty since 1989
- Himeko Nayotake in the Sailor Moon S Movie
- Himiko Shinobibe in the Mashin Hero Wataru Series
- Irina Luminesk in Irina: The Vampire Cosmonaut
- Kyouko Yuuki in Sword Art Online
- Leila in Vampire Hunter D
- Lemina Ausa in Lunar: Eternal Blue
- Lime in Saber Marionette J, Saber Marionette R, and its sequels
- Lina Inverse in Slayers
- Maeda's Mother in Cromartie High School.
- Mako Mori in the Japanese dub of Pacific Rim
- Maria Santos in Yarudora series Vol.3: Sampaguita
- Megumi Amatsuka in Cheeky Angel
- Minky Momo of Marinarsa in Magical Princess Minky Momo (The 1991 sequel series, and no this isn't a case of The Other Darrin since she later meets the 1982 Minky Momo and 1982 Momo is her cousin...kinda)
- Miyokichi in Shouwa Genroku Rakugo Shinjuu
- Momoko Sakurayama in Patlabor
- Momiji Fujimiya in Blue Seed
- Musashi (Jessie) in Pokémon
- Pokémon: Bulbasaur, Pidgeotto, Mudkip, Chimchar, Snivy, Fennekin, and Rowlet.
- Nara-oh Renge and Mii in Legend of Heavenly Sphere Shurato
- Nuku-Nuku in All-Purpose Cultural Cat Girl Nuku Nuku
- Ongo in JungleDeIkou
- Pai in 3×3 Eyes
- Paprika, AKA Dr. Atsuko Chiba, in Paprika
- Patricia Hackman in Super Robot Wars F and F Final
- Ranma Saotome (female) in Ranma ½
- Raven Branwen in the Japanese dub of RWBY
- Rebecca in One Piece
- She also voiced the character Honey Queen in the second movie "Clockwork Island Adventure"
- Rei Ayanami, Yui Ikari, Pen-Pen, Mana Kirishima, and the berserk EVA Unit 01 in Neon Genesis Evangelion
- Rune Balot in Mardock Scramble.
- Shantotto in Dissidia Final Fantasy
- Shirogane/Éléonore Saiga, Francine, Angelina Saiga, the automaton Francine and the fake automaton Francine in Karakuri Circus
- Shuuichi Saihara in Danganronpa V3: Killing Harmony
- Tira Misu in Sorcerer Hunters
- Todomatsu Matsuno in Osomatsu-kun (1988; her first big role)
Megumi Hayashibara's works provide examples of:
- Bread, Eggs, Breaded Eggs: She has voiced a mother (Yui Ikari), a bird (Pen-Pen), and a mother who is also a bird (Raven Branwen)
- Enforced Method Acting: One of the examples of those suffering this before it was prohibited in anime. For a voice-practice of a sad voice, she's told to imagine the saddest moment in her life. Imagining how her grandma died, Megumi was left in tears even after the practice ended, surprising her instructor, Shigeru Chiba. This scene is drawn in Megumi-Toon.
- Out of her entire resume, her Genki Girls tend to be the most remembered not only because of the roles that made her famous, but also due to her own personality being outgoing and energetic to begin with.
- Her original career plan was to save human lives, and that alone requires a good sum of compassion and determination to pursue.
- Her fiery personality was what got her to her What Could Have Been case, as she caught herself into voice acting by pure accident due to submitting a stress-release cassette tape for a voice acting school application (that she randomly caught eye from a magazine ad) of her swearing Unstoppable Rage just for the hell of it because all of the medical schools she applied at the time completely rejected her. She later received admission letters from one medical school, and that voice acting school with free tuition grant, leading her determined to attend both schools at once, mainly to one, take advantage of the voice acting class she received for free, and two, to fulfill her promise towards her parents in getting her medical license.
- Hayashibara is known to have low tolerance for audience with bad manners, and would defend her cast mates if certain types of fans crossed the line in front of her face.
- Playing Against Type: Plays an abusive smother in Wolf Children Ame and Yuki
- Relationship Voice Actor: She and Kōichi Yamadera made their names known through Mashin Hero Wataru, became domestically famous through Ranma ½, and internationally famous through Neon Genesis Evangelion. The two are also officially the highest paid voice actor and actress of the Japanese voice acting industry, reigning as King and Queen of the industry.
- Woman of a Thousand Voices:
- This is the lady whose voice can range from hyperactive to emotionless and sometimes even the cold, harsh one. Oh? Her Hot-Blooded voice is also a hearing to behold.
- The comedic radio-play, Evangelion: After the End, really shows this off: During the play, the normally stoic and quiet Rei finally gets fed up with Asuka's constant pronouncing on other people's intelligence, and goes on an absolutely livid Motor Mouth rant about it.