Miki is a lively high school student, who is on the Toryo High School tennis team. She is cheerful, friendly, supportive, outspoken, tomboyish and good-hearted. On the other hand, she can also be insecure, whiny, clingy, and very emotionally dependent on others. She had a part-time job working in an ice cream parlor, called Bobson's. Later, she works in a small decoration shop.
When she was in junior high, she confessed her love to a male friend of hers named Ginta, but it was a disaster and Miki ended up heartbroken. Eventually she got over it and became friends with him again.
While Miki was in high school, her parents went on a trip to Hawaii and decided to swap spouses with another couple. The other couple had a son the same age as Miki, and they all moved into a large house to live together. That boy was Yuu Matsuura, and Miki started to fall in love with him as they came to know each other better. However, Miki was very uncertain of herself and became jealous because Yuu was always surrounded by other girls, several of them being very beautiful while Miki was only average-looking.In one episode, Yuu confess his love towards Miki and that is the reason he kiss her but Miki slap him because she thinks that Yuu is just fooling her and never be honesy towards her. Ginta confess to her and she is uncertain about the feelings towards Ginta and Yuu. After that she realize that she just scared that she will lost Ginta, her very best friend and she is certain of her feelings toward Yuu.
When Yuu is depressed after mistaken his father, Miki convince him and confess her love to him. Yuu was surprised and they start their relationship as a couple. Their problem start when Yuu participate a commercial with Suzu. Miki starts being jealous and Suzu intents to make Yuu and Miki to break up. Miki wants to go on a trip with Yuu so she start to do part time job in an ice-cream shop. She meet Kei there and Kei fell in love with her eventhough she does not realize it. They nearly break up because of Kei and Suzu. However they make up again after Yuu is back from the trip. When Yuu is back from the trip he introduce Anju,his childhood friend and first love to Miki but he explain to her that now Anju is just his bestfriend. One day, Anju find Miki and tell her that she love Yuu. Miki was surprise and she don't know what to do. On the Christmas Eve, Yuu went to meet Anju and Miki felt sad when she saw Yuu was so concern about Anju and she mistaken Yuu likes Anju.
Their problem occurs again when Yuu went to study abroad in New York. Miki misses Yuu and decided to go to New Yok to visit Yuu. However a girl name Jinny fell in love with Yuu and she she had one night stand with Yuu. MIki was very sad and decided that she will go back to Japan. Meiko tried to contact with Yuu but she can't get in touch in with him because he is not in the campus. Yuu went to Brian's house. Yuu rush to the airport when he received Meiko message. Miki and Yuu break up. Back in Japan Miki is with Kei until Yuu is back in Japan for summer vacation with Anju. She mistaken Yuu and Anju are a couple. Miki,Kei, Yuu, Anju and the others went for camping. Miki realize that she could not forget Yuu and she make up with Yuu. Their relation does not last long because Yuu mistaken that he and Miki are siblings and wantes to break up with her.
Miki went to America to find out the reason why Yuu wants to break up with her. When Miki knows the fact she when to a dangerous street that has a lot of villians there. Yuu is concern about Miki and went to find her. They decided that eventhough they are siblings they will stay together. Miki's and Yuu's parents went to America because they are concern about Miki. Miki and Yuu know that they are not siblings. At the end, Miki and Yuu married
Voiced by: Ryōtarō Okiayu (Japanese); Michael Lindsay (English)
The male protagonist of the series, Yuu is also the title character, as Miki gives him the "Marmalade Boy" moniker as she thinks that he is like marmalade - pretty looking, and sweet only on the surface, yet bitter.
Compared to Miki, Yuu's character is almost a complete opposite to hers, as he tends to be more detached, less emotional, and less open about his feelings. He admits to admiring Miki's ability to show her emotions clearly, and it being one of the reasons he fell in love with her. Numerous people comment throughout the series of how he has a good "poker face." [citation needed] It is shown that Yuu is smart and naturally athletic, being able to excel in almost every sport although he did not join any clubs in order to focus on his studies. Yuu's dream is to become an architect and he leaves to attend St. Andrews high school near New York City to study it there. Yuu teases Miki a lot, but this is his way of showing affection for her. His first kiss with Miki is a complete surprise for her because she had only met him a few days prior at an introductory dinner attended by both their families. The Marmalade Boy Movie, which is a prequel to the TV series and set a few days before this dinner, reveals that Yuu fell in love with Miki before they actually met. It shows that he saw Miki when she was out and followed her, witnessing her interactions with the Gastman Team, all without her knowledge.
Miki's best male friend and a member of the Toryo tennis team. Miki has had a crush on him since junior high and confessed her feelings to Ginta in a note. However, the note was found by Ginta's classmates, and Ginta downplayed it, without knowing at the time that she was watching, although he felt the same way about Miki.
Although he did find out that Miki had witnessed his denial of any interest in her, he was unable to tell her how he really felt until high school. The romantic tension between them comes to a head with Yuu's appearance, which makes them realize that they still have feelings for each other. He decides to go along with Yuu's ex-girlfriend Arimi's proposal that they pose as a couple in order to drive a wedge between Miki and Yuu. In the process however, he starts to develop genuine feelings for Arimi, which she later reciprocates.
Voiced by: Wakana Yamazaki (Japanese); Kate Higgins (English)
Miki's best female friend Meiko is the only child of wealthy parents and is very mature and beautiful. However, her family life is troubled because her parents are unfaithful to each other and constantly argue. She falls in love with Shinichi Namura after realizing that he has the maturity that she craves, but their relationship as teacher/student proves to be a huge hindrance.
Voiced by: Aya Hisakawa (Japanese); Carrie Savage (English)
Arimi is a former classmate of Yuu's at his previous high school. She convinces Yuu to be her "boyfriend" for three months, during which they act as a couple on a trial basis. Arimi attempts to make Yuu to fall in love with her during this time, but fails. At the end of the three months, he still thought of her as a friend.
Miki's indecisiveness about Ginta and Yuu frustrates her, as she does not think that Yuu deserves someone who cannot commit to one person. Arimi teams up with Ginta in an attempt to drive Yuu and Miki apart from each other. However, she eventually realizes that Yuu's behavior around Miki indicates that he does like her, so she stops her pursuit of him. Some time later, she develops feelings for Ginta and they become a couple.
Voiced by: Kazunari Tanaka (Japanese); Tom Gibis (English)
Tsutomu is Ginta's cousin and a classmate of Arimi's. He has had a crush on her for a very long time. Tsutomu sees himself as Ginta's rival, and Arimi teaming up with Ginta to split Yuu and Miki frustrates him even further. In the anime, after Arimi's definitive rejection Tsutomu befriends a girl named Yayoi and they start dating.
Voiced by: Shinichiro Ohta (Japanese); Jack Aubree (English)
Satoshi is the student body president and a third year student. Many girls are interested in him, but he is only interested in Meiko, and tries to get her to like him in place of Namura. However, his crude sense of humor does not impress Meiko, who thinks he is an irresponsible playboy. They go out for a time, but Meiko is unable to overcome her feelings for Namura. Satoshi tries several times to make her forget Namura, but following the "Hiroshima arc" he sees that he has no chance to win her over and stops his romantic pursuit of Meiko, staying friends with her instead.
Satoshi is the first person to notice Yuu's interest in architecture. His initially unusual behavior towards Yuu arouses Yuu and Miki's suspicions that he is gay and has a crush on him, which he uses to his advantage. Satoshi and Yuu eventually come to an understanding however, and Satoshi helps Yuu uncover the truth of who his biological father may be, as he suspects that his father Yoshimitsu is a potential candidate. Although it is later revealed that Yoshimitsu is not Yuu's true father, but Satoshi and Yuu stay best friends after this.
Voiced by: Sakura Tange (Japanese); Mia Bradley (English)
Suzu is Satoshi's younger cousin who is a well-known teen model. Suzu fell in love with Yuu immediately when she saw his picture, which motivated her to do the cosmetics commercial that she was shooting when she found out that he would be in it. Through Satoshi's efforts, Yuu also became Suzu's math tutor. Suzu tried to express her feelings for Yuu, but he was not interested in her and only saw her as a kid sister. She also tries to tear Yuu and Miki apart after mistakenly believing that Miki is cheating on Yuu, but fails. She develops a love/hate relationship with Kei.
In the manga, Suzu doesn't want Yuu for herself; instead she attempts to hook Yuu and Meiko up, after mistakenly believing that Meiko is in love with Yuu. Nevertheless, she fails.
Voiced by: Akira Ishida (Japanese); Henry Banks (English)
Kei is Miki's coworker at Bobson's ice cream parlor who is a talented but troubled pianist. He also falls in love with Miki, and his methods to get her away from Yuu almost bring him success after he uses Miki's lost medallion (which had a picture of Yuu) to fabricate a lie about Miki's true feelings for him. However, this also fails after Yuu makes a trip outside of Tokyo but cannot enjoy since he misses Miki too much, and Miki forces herself to see the worst side of herself. When they see each other again, they come back together. Nevertheless, Kei still confesses his love for Miki at Christmas; and after some convincing by Miki to regain his confidence in music, Kei quits his job at Bobson's ice cream parlor and says goodbye to Miki, promising to return soon.
In the anime, a much more mature Kei reappears later, offering Miki his sincere and unconditional support after Yuu goes to study abroad. He says he does not need to have Miki forgetting Yuu completely, since he's happy to help her through her ordeal. Miki appreciates his company and even dates him briefly, but he cannot compete with Yuu. It is hinted at the end that he may or may not get together with Suzu Sakuma.
Voiced by: Tōru Furuya (Japanese); Jack Aubree (English)
Namura, affectionately known as "Na-chan" by his students, is a former Toryo student who returned to his alma mater as tennis coach and English teacher. He develops feelings for the student Meiko Akizuki, which are reciprocated. However, because she is a student they must keep their relationship secret. The relationship is eventually discovered, embroiling Namura in a big scandal.
Finding his position at Toryo untenable and fearing he'll be a hindrance for Meiko, he resigns and returns to his hometown of Hiroshima in order to study real estate and take over the family business. Namura tries to push Meiko away from him no matter how much he loves her, thinking that he cannot allow her future to be tainted. Ultimately, Meiko proves him wrong, and they reach an agreement: as soon as Meiko graduates and turns 17 (the age at which she can marry Namura without her parents' approval), she will come with him to Hiroshima not only marry him, but also to study literature and become a writer. At the end of the series, the agreement is filled and they marry.
Voiced by: Hideyuki Tanaka (Japanese); Will Barret (English)
Miki's father and an accountant who works at a bank. He married Miki's mother Rumi after breaking up with his old girlfriend Chiyako and helping Rumi over her own break up with her boyfriend Youji. They moved to England and had Miki there, then returned to Japan. Later, he and Rumi reencounter Chiyako and Youji, reach an agreement, and swap spouses.
Voiced by: Yoko Kawanami (Japanese); Wendee Lee (English)
Miki's mother, infamous for her bad cooking. She is cheerful and sweet, and like her ex-husband, a little child-like as well. She works at a cosmetics company. She was married to her old friend Jin Koishikawa, later divorced him on good terms, and married Youji Matsuura, her old flame.
Voiced by: Bin Shimada (Japanese); Conner Holly (English)
Yuu's father, who works at a trading company. He is mature and quick-witted, like his ex-wife and now best friend Chiyako. He is also good at math, yet horrible at video games. After divorcing Chiyako, he married Rumi.
Yuu's mother, who works as an executive in an alcoholic beverage company and is a very good cook. She also gets along well with Miki, yet tries to not be pushy on her, which Miki appreciates a lot. She had a short-lived affair with her former boss, Yoshimitsu Miwa, and lost the baby that she and Jin were expecting during college. This lead Yuu to think that Youji is not his true father.
