A 12-year-old girl named Mitsuki Koyama dreams of becoming a great singer and of her childhood friend, Eichi. Unfortunately, she has sarcoma, a tumor in her throat, preventing her from becoming a singer. Moreover, her grandmother does not want her to have anything to do with music. Mitsuki gets an audition at Seed Records Studio. She tries to persuade her doctor, Wakaoji, into taking her there, but she fails. What's worse is that a pair of Shinigami, Takuto and Meroko, appear and tell Mitsuki that she has only one year left to live. Not fearing anything anymore, Mitsuki runs off to the audition. Takuto and Meroko decide to help Mitsuki by transforming her into a 16-year-old!

Meroko and Takuto argue about letting Mitsuki audition. Mitsuki, Meroko, and Takuto talk about why she wants to become a singer. The Shinigami find out about Eichi-kun, and then Takuto and Meroko switch sides of the argument. Takuto thinks that's an immoral reason for singing, gets angry at her, and flies off. Meroko reads Mitsuki's fortune and says that it will be her lucky day. Meroko and Mitsuki go shopping, and then Meroko pretends to be Eichi-kun. In the end, Mitsuki tells Takuto that she really does love to sing and it's not just for Eichi, and the two make up.

After a day of school, Mitsuki gets a call from Dr. Wakaoji. He explains that Mitsuki's new manager Masami Oshige wants to meet her at the hospital. However, Mitsuki will have to be in her 16-year-old form in front of the manager, and she'll have to be in her regular 12-year-old form in front of Dr. Wakaoji, with them both in the same room. Since telling the truth isn't an option, Meroko takes it upon herself to solve the problem. In the end, Mitsuki and the shinigami manage to trick them.

Mitsuki's debut CD is already being discussed by her producer, Mr. Takasu. Takasu wants her to sing a pre-written song for her debut, but Mitsuki wants to sing a song with her feelings in it. So, now Mitsuki has three days to write her own song.

Mitsuki's first job starts out rough because she worries about whether or not she's acting her age. But, after talking to three high school girls, she manages to get through the day, now reassured of herself.

Mitsuki and Takuto (pretending to be a doll) go to the studio to do a recording while Meroko stays at home, posing as Mitsuki. While Mitsuki learns what to do in a recording booth, a little girl named Nanami sneaks in and takes Takuto away. When Mitsuki finds them, Nanami refuses to give Takuto back.

It's time for Full Moon's first live performance! But when a girl from the past questions Mitsuki's abilities as a singer, she begins to doubt herself.

Full Moon's debut maxi single, "Myself," is now on sale! The good news is that it's a smash hit! The bad news is that no one at Mitsuki's school seems to be talking about the CD, and Mitsuki doesn't have any friends nor the confidence to spread the word about her single.

You'd think that since "Myself" is such a big hit, everyone must have listened to it. But, Mitsuki soon learns that Dr. Wakaoji has not listened to "Myself," and she really wants him to hear it.

Mitsuki gets to debut on TV on a show starring Fuyuko Komaki. However, Komaki doesn't seem to like Mitsuki very much.

There is a photographer named Saegusa who has a reputation of destroying celebrities' images with his pictures. His next target: Full Moon.

Takuto gets mad at Mitsuki for drawing a terrible picture of him. He fies off and Meroko follows. Meanwhile, an old man collapses in frotn of the house, and Ms. Tanaka takes him in. As a show of gratitude, the old man gives Tanaka the Saint's Stone, a big rock that has the power to expel Shinigami. So, naturally, the stone prevents Takuto and Meroko from getting into contact with Mitsuki, which is bad because she has a job to do later.

Mitsuki holds a Full Moon mini-concert at the Hiiragi Preschool. All the kids love her except for this one mean little boy, Taiki, who looks very similar to Eichi. As the day goes on, Taiki does a lot of bad things to Mitsuki from lifting up her skirt to stealing her stage costume to wrecking the entire concert. Despite all that has happened, Mitsuki still feels that Taiki did all this for a good reason.

Ms. Oshige is sick in the hospital today. So, Mitsuki will have to deal with her clumsy substitute manager, Kotarou Akiba.

It's summertime, and Mitsuki gets a job by the beach. When Mitsuki gets harassed by three boys, an attractive young man named Murakami saves and befriends her. However, Takuto doesn't trust the guy one bit. He wants Mitsuki to not see him again, but she doesn't want to do that. As a result, Takuto flies off on his own (again). Mitsuki is on break from work the next day. Murakami invites her to tour the place on his yacht. Out of spite of Takuto, she humbly accepts. Unbeknownst to her, Murakami plans to kiss Mitsuki and capture it all on videotape.

Mitsuki gets an audition for a shampoo commercial. It's Meroko's turn to go out with Mitsuki while Takuto stays home. Unfortunately, Meroko gets her lost when finding the site for the audition. What's worse is that the girl from the singing audition back in the first episode has returned! Her name is Madoka Wakamatsu, and she's willing to do anything to keep Mitsuki from winning the audition.

The judges have come to this conclusion: a camera test for Full Moon and Madoka will be held the day after tomorrow. From there, either Full Moon or Madoka will be chosen for the job. When Mitsuki asks about Takuto's past, Takuto gets mad at her and flies off, and Meroko soon follows. Meanwhile, Madoka gets opportunities to help her image and get the job. Mitsuki goes outside and blows her whistle so that Takuto will come back. Her illness causes her to collapse and be taken to the hospital. The next day, she gets out of her hospital bed to go to the camera shoot, losing her whistle.

Takuto finds Mitsuki, transforms her, and goes with her to the commercial audition. In Meroko's Shinigami handbook, the word, "Audition," appeared backwards on a page, meaning that the upcoming audition will cause an early death. So, Meroko tries to stop Mitsuki and Takuto from making it to the audition.

Mitsuki has arrived at the Mermaid Tear Image Character Audition, only to find out that she is late and that Madoka has won by default. Things get even worse when Oshige and Dr. Wakaoji catch up with Mitsuki. It seems that Oshige is looking for the 16-year-old "Full Moon" Mitsuki, and Wakaoji is searching for the 12-year-old Mitsuki. She and Takuto run away from the two. However, Mitsuki is depressed about how Oshige and Wakaoji may discover that the 16-year-old Full Moon and the 12-year-old Mitsuki are the same person, how she can't go back to them, and how she may not get to be Full Moon anymore. Meanwhile, the news that Full Moon has quit the business floods the media. Mitsuki hides out by the shore, where she hears her song, Myself, sung by Takuto.

Despite being scolded by her grandmother and telling Oshige and Dr. Wakaoji everything that has happened to her, everything seems to be back to normal for Mitsuki. But there's something missing from all this; where's Meroko? Why, she's playing basketball at a school gym, of course!

Full Moon is back, and she's going to appear on a TV music program. Despite all the gossip, she's not going to be held back. That is, until Madoka decides to do something about it.

Full Moon's first solo live concert is going to be held soon! The theme is Moon and Stars. Everyone has worked their hardest for this event, but unfortunately, the site of the concert has been canceled at the last mintue!

Ms. Oshige decides to live in an apartment that's close to Mitsuki's home. She calls Mitsuki, Takuto, Meroko, and Dr. Wakaoji over to help her move in. But, when Ms. Tanaka sees Wakaoji and Oshige together, she takes it the wrong way and thinks that Oshige is Wakaoji's fiancee! So, Tanaka challenges Oshige to see who is more suited to being Dr. Wakaoji's wife!

Mitsuki second single will be "Eternal Snow," a secret song by the legendary band, Route L. Coincidentally, Madoka chooses to debut as a singer with that very song!

Mitsuki needs Dr. Wakaoji to produce her song, but she doesn't have the courage to ask her. When Oshige and Meroko try to persuade Wakaoji, he declines. Even when Mitsuki finally gathers the strength to ask him, he still declines. But, after hearing Takuto's words, Wakaoji thinks heavily about this. After a few days, Wakaoji has decided to become Mitsuki's producer.

Wakaoji tells Mitsuki to think about what kind of message she wants to send when she's going to sing "Eternal Snow." So, Mitsuki, Takuto, and Meroko rummage through the Kouyama family's old things to see what kind of message Mitsuki's father wanted to send. They then find a jeweled music box that plays the "Eternal Snow" melody.

Fearing that she may lose to Full Moon, Madoka gets a reporter to take a photo of Full Moon and Wakaoji together. This starts a scandal about Full Moon and Wakaoji having a secret date.

Mitsuki gets fan-mail from a girl asking for her advice in love. Mitsuki soon realizes that her friend, Kumi, is the one who sent that mail! Apparently, she has a crush on a boy named Machida, but she's clueless on how to let him know about her love for him. So, she turns to Mitsuki, who she assumes is the master of love.

Mitsuki/Full Moon and Takuto go to the release of Full Moon's second single. Once again, Meroko stays at home. But, she gets some unexpected visitors: the sadist Shinigami, Izumi, and his partner, Jonathan. By order of the chief, they came to investigate if the rumor was true - Meroko and Takuto were using their powers to help a human child. When Izumi and Jonathan decide to check out Full Moon's release of her second single, Takuto and Meroko have to keep them from knowing that they are helping Mitsuki.

Mistuki gets a visitor; it's her teacher from her old orphanage, Kazumi-sensei. She's visiting from her home in America. Knowing of Mitsuki and Eichi's love for each other, Kazumi-sensei will gladly look for Eichi in America for Mitsuki. All Mitsuki has to do is make some kind of letter, saying what she really feels about Eichi.

It's not all fun and games at this year's college festival. Takuto transforms into a human to protect Mitsuki from some muscle-bound fanboys.

Things haven't been going well for Madoka after she lost to Full Moon; she got a new manager, she has bad jobs like cheap commercials, and people are talking bad about her behind her back. Mitsuki later finds herself in Madoka's home, where she discovers a little more about her.

Mitsuki's illness grows worse, and Dr. Wakaoji isn't around in her time of need, especially when Mitsuki's grandmother wants Mitsuki to receive the surgery.

Mitsuki meets a man named Sanada. He is able to see Shinigami like Takuto and Meroko. It is due to the fact that Sanada will soon die.

Mitsuki is haunted by images from a dream she had about Izumi. But, she soon cheers up after getting an e-mail from... Eichi-kun!?

Full Moon has been nominated for the Fantasia Music Festival's New Artist of the Year award! Takuto and Meroko contemplate on whether or not they should tell the truth to Mitsuki about the e-mail from Eichi.

Christmas time is near, and Mitsuki is inviting her friends to a party at Oshige's apartment. She is also giving out presents. Meroko decides to knit a muffler for Takuto as a present. Madoka's debut CD is finally released on Christmas Eve.

Although Mitsuki and the rest are ready to go to America, there is still the matter of asking Mitsuki's grandmother for permission. Dr. Wakaoji tries to explain to Mitsuki's grandma that there is a doctor in America that can perform surgery on Mitsuki and not lose her voice in the process. However, she does not like the idea. Mitsuki decides to go to America anyway. However, she ends up meeting with grandma's childhood friend, who tells her about her grandma's past.

Mitsuki and the gang are now in America, and they are currently staying at Kazumi-sensei's home. Mitsuki and Eichi's past is further revelaed. Also, Takuto is feeling rather melancholy.

The gang decides to do a little sight-seeing, but there is a group of pickpockets around. They steal Mitsuki's pendant in the process.