She is cheerful and optimistic, but lacks the sophistication and "common sense" to deal with the royalty (due to her being a country bumpkin). She quickly gets acquainted with the other Corals and Pearls in Garderobe and becomes good friends with most of them, mainly Nina Wáng and Erstin Ho, her roommates.
It is hinted in the series that despite her behavior, she may be the true Queen of the Windbloom Kingdom - a fact that Sergay Wáng believes as he's found proof for later on according to an eyewitness he contacted. This was strengthened when Arika opened an ancient weapon called the Harmonium which required a player, conductor, and protector, roles which those of the Windbloom bloodline can fulfill.
As time passed, Arika started losing her optimism in being an Otome as she learns more about the past, specifically the Dragon King War in which numerous Otomes, many who were friends with each other in Garderobe, fought each other and died. As more time passed by, Arika started to grow an affection towards Sergay despite the fact that he was 10 years older than her. When Akane chose love over being an Otome, Arika followed suit and went out to confess to Sergay. Fortunately for her, right before he kissed her, Sergay rejected and insulted her mother in order to protect her. Sadly, Arika was devastated by this rejection and zoned out many times but eventually pulled through after a talk with Mashiro who was suffering similarly and the two promised to be an excellent Otome and Queen respectively.
This was not the last for Arika as Schwarz launched an attack and it was later revealed that Erstin, her best friend upon who she trusted, was part of the cult. When Sergay took a shot meant for Arika, a handkerchief that she sent to her benefactor came out and she realized Sergay was her supporter the entire time. Nina, angry at this revelation, attacked her with her Ultimate Black Diamond, but Erstin's SLAVE took the shot and hence also caused the girl's death. In the aftermath, Arika is found by the Aswad Knights in a doll-like state, continually questioning what Otomes are. Nevertheless, after some talk with Mai and Midori, Arika renews her contract with Mashiro and trains with Mai to become a better Otome.
When Miyu returns to the scene in later episodes, she confirms that Arika is Lena Sayers' daughter, in addition, she is also a descendant of Alyssa Searrs. (Her hair glows gold when Miyu looks at her, the same way as Alyssa's did in My-HiME.) Miyu found the Sapphire Gem in Artai which was about to be sold and gave it to Arika's grandmother for safekeeping. Miyu also revealed that Arika is not, however, the true Queen of Windbloom as was expected. Mikoto fights with Arika to test her and the latter is defeated soundly. Mikoto ends up training her to use the Sapphire GEM more effectively.
Arika pulls through and in the end, defeats Nina and the Harmonium with her powered-up robe. Effectively defeating Nagi and as Nina fell into the atmosphere, she followed with her and saved her. In the aftermath, Arika helps Mashiro's dream come true by planting a large flower petal on top of the castle according to Mashiro's plan and remains as her meister Otome.
The matter of who her father is is one that was never raised, at least in the anime, and is a subject of speculation. One theory, apparently supported by clues in the show, is that he is Rad/Reito. Also, since the release of My-Otome 0~S.ifr~ episode 2, people suggest that Shiro might be Arika’s father.(Due to physical similarities)
One year after the end of the TV series, the first episode of My-Otome Zwei sees Arika called to action as part of a team of Otome who destroy the asteroid Thron 1, which is heading for the planet, by deploying "Meteor Breakers" or explosive lances in an effort to fracture the asteroid enough so that the pieces will burn up in the atmosphere. When the meteor inexplicably changes course Arika goes after it and calls upon the second form of her robe by getting Mashiro's verbal approval and shouting "Soten!" in a transformation referred to as "Materialize Zwei" (Zwei being German for "two"). Using the Sword of Akatsuki, she gains enough strength to destroy the meteor, but as she celebrates a black-winged shadow appears behind her. Note that her Coral earring has been replaced by a Meister-looking one. However, it is different earring than the one used by her mother, the previous Blue Sky Sapphire.
She awakens at the palace, at first believing it was a dream until Miss Maria shows her a newspaper proving otherwise (the headline of the newspaper reads "Arinko, Save US! Ms. Arika Yumemiya Make a GreatCoup"). Miss Maria also reminds Arika that she is still under her tutelage, since she does not have enough credits yet and promptly assigns Arika laps and reading transcriptions. Several fans have also noticed that Arika's bust has received an upgrade in the one year hiatus of the story. The next scene features Arika writing "a letter from her heart" to the absent Nina; updating her friend on the events of the past year and Mashiro's growing leadership. She then sees a group of workers demanding higher wages and talks to them, much to Mashiro's annoyance; as she had been in negotiations trying to keep the economy stable. Throughout the episode Mashiro and Arika butt heads several times on issues such as this, with Mashiro frustrated at Arika's naivete.
When a Slave appears at the Black Valley and Arika rushes to the scene to protect Mashiro and fight with Mai at her side, finally defeating the Slave after using the Zwei robe. After Arika reprimands Mashiro for ordering Natsuki Krueger to go to the Garderobe before saving innocents trapped by the destruction the Queen becomes frustrated enough to yell at Arika, breaking the connection required for the Zwei robe. The end of the first episode sees Mashiro disappear into the collapsing Black Valley with the black-winged figure from the beginning of the episode looking on from a distance, which at this point has turned Miyu, Shizuru and Miss Maria to stone and can seemingly imitate the powers and appearance of anyone it has had contact with.
In the second episode Arika travels to Aries with Mikoto the cat while trying to find Mashiro, but ends up being a hostage in a bus hijacking by terrorists. President Yukino Chyrsant eventually offers herself up as an exchange for the civilian hostages in order to buy Haruka and Chie time to come up with a plan. During this time Arika asks Yukino about her relationship with Haruka and how they get along despite their differences. They are eventually freed by a combined attack, at which point the Unknown Entity attacks and petrifies Haruka.
In the third episode Arika is with the other Otome at the SOLT in the bathhouse and attempts to sneak away before being stopped by a drunken Ahn Lu. At the conclusion of the episode the CHILDs around the world start to awaken.
In the fourth episode Arika continues to search for Mashiro and it informed by Gal that Midori Sugiura wants to see her. She talks to the Boss and receives a letter that Mashiro has written earlier addressing that she is on the Black Valley. Arika is then confused on how to get to the island, but Mikoto the cat alerts a dophin with a similar earring to it. When Mashiro is attacked by Yuna in the form of Fumi Himeno, Arika comes and temporarily distracts Yuna. She transforms and fights with Yuna. Later when Yuna is about to kill Arika, Nina Wáng steps in and stops Yuna. Arika is happy and attempts to hug Nina, but Yuna swats her away. Arika and Mashiro have a heart to heart and slap each other in order to regain the true power of the Blue Sky Sapphire. Arika and Nina fight until Natsuki Krueger alerts them on how to stop Yuna. Yuna then sucks in Mashiro and takes a similar form to Fumi's Child, (see Mashiro Kazahana). Arika destroys Yuna with a Bolt from the Blue and rescues Mashiro. After, in the credits, Arika shows Mashiro what the world looks like from space.
In the Otome manga, Arika's role is somewhat reduced into that of a comedy sidekick, in favor of a different leading character. Her childishness and unawareness of things is nearly taken to a level of being mentally retarded - a topic which the school administration keeps bringing up from time to time. One manifestation of this was her ignorance of the uses of a hotel room. On the other hand, she often displays remarkable talent in actual battle, leaving her fellow students far behind.
When she first appears in the manga, it is after Mashiro accidentally bumps into her. Arika is already an Otome, but ranked at the low position of No. 51. A stickler for grammatical accuracy, she takes it upon herself to correct Manshiro's various language-related gaffes.
She often sleeps in class. Lacking the sponsorship of Sergay that her anime version had, she has to take on multiple jobs to pay for her education, to the detriment of her results.
She was the first to respond to the attack on the Artai embassy by Schwarz, attempting to battle Lumen bare-handed.
Although Mashiro had made temporary contracts with her using the Blue Sky Sapphire before, it is not until Chapter 23 that she and Mashiro formally make their contract with the Blue Sky Sapphire, as opposed to the earlier Episode 7 in the anime. This was also at Lena's urging, instead of being accidental like in the anime.
Arika had always been in search of her parents and a Star Wars-esque revelation by Rad that he was her father caused her much concern. The Otome manga's version of Kazuya led her to go to the Black Valley in search of the truth, where she found Lena as well. Initially she refused to believe that Rad was her father, but she finally acknowledged him before he died.
When she was younger, her hometown was attacked and razed by mysterious assailants, a repressed memory that was freed when she saw Kagutsuchi, leading to her going hysterical and speaking of dragons and calling for her mother and grandmother before fainting. She was left behind to go with Midori and the refugees, but wanted to go back and fight. At her insistence, Midori lent her the REM so she could Materialise. Although she lost her power once again due to the REM having reached the limit of its use time, she gained the Ultimate form of the Blue Sky Sapphire Robe by linking hands with Manshiro as Lena instructed. With this new power she beats off Mai and gains temporary victory, only to lose Lena to her sacrificial entry into the Shinso core.
Nevertheless, she continues aiding Manshiro in battle. When Mashiro trapped Mashiro in a projection within the Fuuka Academy and told her and Nina to battle it out in order to save him, she chose not to. Mai, renewed, obeys Mashiro's instruction to attack and Arika went to confront Mai and Kagutsuchi alone on the basis of what she believed was Manshiro's being her younger brother. As she was about to sacrifice herself to kill Mai, however, Mashiro saved her.
Her belief that she and Manshiro were siblings was shattered by Sergay's revelation that Manshiro had only been given into Lena's hands by Emperor Tate and Empress Mai. Shortly after, Fumi Materialized and she proved no match. However, the intervention of Erstin saved her and she lent her power to Manshiro to conduct the Trinity Lover Strike that destroyed Fumi and the revived HiMEs.
Arika carries the Blue Sky Sapphire (蒼天の青玉 Sōten no Seigyoku) as a necklace which was inherited from her mother, the previous Blue Sky Sapphire and Otome to the Windblooms. This gem has been activated a few times in the series when Arika was in danger and by materializing a robe when she didn't have any nanomachines in order to keep her airborne and to blast a SLAVE away. When it was used against the SLAVE, it released two gems, one for Arika and one for Mashiro, which went into her ring. The two make a contract and defeated the SLAVE. Unable to remove the gems the two decide to keep this a secret from the Garderobe staff, but when Schwarz and Artai launch an attack on Windbloom, the Gem is brought back and Arika utilizes the robe though according to Miyu she has not tapped into its full potential and still requires training.
As it turns out, the Sapphire's true power is the robe, Ultimate Blue Sky, that her mother, Lena, wore when she was an Otome. This robe was instead blue with a green cape on the back. Miyu revealed that the power could only be unlocked once Arika accomplished one final goal, to kill/free her mother from Schwarz's capsule.
While in a Meister Robe, Arika wields a double bladed crystal lance as her Element; her primary attack is called "Bolt From the Blue." Her enhanced mode special Element is the Sword of Akatsuki (a reference to Gear Fighter Dendoh, which had a similar weapon). In addition, her hair turned gold like with her ancestor, Alyssa. Screenshots of the My-Otome Playstation 2 game "Otome Butou Shi" showed Lena using a Bolt from the Blue even larger than herself and suggested that Arika still has not achieved the full power of the Blue Sky Sapphire. However, by the time of the OVA, Arika has mastered this power as well.
In My-Otome Zwei, Arika's Robe has changed a little. By default it is an altered form of her incomplete robe before she freed her mother, with blue highlights on her abdomen, and material covering her thighs. She can access her mother's robe using the key phrase "Materialize Zwei." Here she has access to a greater amount of power, and the Sword of Akatsuki.
The manga version of the Ultimate Blue Sky Sapphire uses a much smaller version of the peculiar weapon that anime Lena's Ultimate Blue Sky Sapphire uses instead of the Sword of Akatsuki, which is a different object in the manga.
Although Arika's real appearance in My-HiME was a 2-second cameo at the very end of the final episode, Arika has made three other appearances in the universe of My-HiME.