Aishia

Aishia is Rio's contract spirit as well as a high rank spirit, of which their existence are incredibly rare. She has been contracted with Rio since the start of the novel, during the time Haruto's memories awakened within Rio.

Aishia was the one who taught Rio the Spirit Arts before he sets foot on Seirei no Tami after he fled from the Strahl region due to being framed for the cliff incident.

Prior to her awakening in her humanoid spirit form, Aishia spent the 3 preludes arc mostly by sleeping and residing within Rio. He would occasionally hear Aishia's voice briefly in a form of inner-monologue, where she tries to help and guide him out of his predicament. Aishia would eventually manifest herself and wakes up next to Rio on his bed after he successfully rescued Miharu, Aki and Masato from the slave traders.

Appearance
Aishia is stated many times in the story as the most beautiful female in the series. She has a very divine look as said by Rio seeming almost artificial in a way, her beauty leaving a cold and fleeting impression. Aishia has extremely long peach-colored hair reaching down her knee and gem-like eyes of the same color.

Personality
Aishia is a caring and curious girl. She is devoted to Rio and will always accept him. She always wants to try living the same as humans do, eating good food, taking a bath, and wearing a cute dress. Though she's pretty blunt with her words, she has a weak expression, almost expressionless most of the time, and she speaks in a monotone intonation.

According to Dryas, it's unnatural for Aishia to show a lack of expression as a spirit's personality should mature and upon becoming a high-class humanoid spirit, they should already have a full personality. Yet, although already a humanoid spirit, Aishia is like a Medium-Class spirit mentally, that is unless, being  an expressionless character is indeed her personality. Also, when she manifested, she had no memories aside from knowing all about Rio.

Pre-Awakening
Aishia first appear in Rio dream at the day Haruto memory awaken in him, she told  Rio about his ability to use Spirit Arts, then later in the day of Hero summoning, Aishia notifies Rio using telepathy about Miharu arrival and told him to head where she lands to save her from being enslaved.

Awakening
The sign of Aishia awakening happen at the same time of the hero summoning where Rio senses a warm magical build up inside him, Aishia truly awakens in the next morning, appearing naked in Rio's bed, witnessed by Miharu, after explaining the circumstance to Miharu, he gives her name, Aishia, and then they start living in rock house with Aishia helping Rio teaching the three Japanese, Strahl language.

Spirit-folk Village
Aishia first visits Spirit Folk Village, when Rio went to the village for dropping Miharu, Masato and Aki in their protection. There she meets Latifa and Spirit Folk trio for the first time. They all get infatuated with her otherworldly beauty as well as her strong spirit aura. Latifa manages to muster her courage and asks her name. When Latifa asks her can she call her by her name, she allows her. But Spirit folk trio chooses not to call her by her name instead they choose to call her Aishia-sama, as humanoid spirits are worshipped in Spirit Folk Village. She seemed confused when everyone in the spirit folk village looks at her with reverence. There she meets her fellow humanoid spirit Dryas for the first time. When asked which all elements she can use, she replies she can use all the elements that Rio can use, at this answer all the elders and Dryas gets surprised as it is not possible for the high-ranking spirits to use all the elements as Dryas herself can only use water, air and earth.

The elders and Dryas think that Aishia is not some ordinary spirit because even the previous six high ranking spirits were not able to use all the elements. Dryas thinks in a straight up fight, she will lose against Aishia. When Rio told Dryas Aishia does not have any memories before her awakening, she then takes Aishia to her cave in the Great Tree to teach her about all the skills that spirits can use like telepathy. Thus, she spent quite a lot of time with Dryas when she was in village.

After a few days, she left the village to travel with Rio towards Strahl Region where Celia was.

Wedding Crasher
Aishia helped Rio in gathering info about how and why Celia is getting married to Charles Arbor. Before the abduction Aishia used telepathy to inform Celia about Rio's presence among the crowd. When Rio was distracting the soldiers, Aishia took Celia outside of the capital and thus helped Rio in rescuing Celia from her unwanted marriage.

Amande's Trouble
Aishia notified Rio about the monster attack on Amande. Also when Rio decided to chase Lucius, she along with  Celia protected  Liselotte and others from revenants who had invaded her mansion. She successfully repelled all monsters and even went on to kill Alphonse who had become a black skined revenant.

Galarc Ball
Aishia travelled with Rio and Miharu in her spirit form, She acted as the messenger between Rio and the rock house group. After Rio, Miharu and Satsuki  met  Takahisa she went to Rockhouse to inform  Aki and  Masato about  Takahisa's whereabouts and also to inform that Satsuki would be visiting rockhouse later. She also played a fundamental role in Miharu's rescue and she also helped Miharu in conveying her feelings to Rio.

Abilities
Spirit Arts: As a high-class spirit, Aishia is the pinnacle of Spirit Arts, moreover, she also a universal attribute spirit, meaning that she can use all attribute in their strongest state.

Martial Art: Aishia possesses the same martial art with Rio through some kind of imitating ability.

Telepathy: By creating a path that connects their soul, Aishia can communicate with the one connected with her telepathically, while her main path is her contract with Rio, she also can create a temporary path when getting separated from Rio, her telepathy range can encompass an entire city.

Dream Creator: Aishia can create a dream and show it to someone that's sleeping, it can range from good dream to bad dream and the one that experiencing it can only follow the dream without any ability to change anything in it.

Trivia

 * Aishia name comes from the Spirit folk language that means a warm Spring and A Beautiful Spring, with the latter meaning sharing the same meaning with Miharu's name.
 * In the anime version, Aishia started to show her physical body when Rio was in the Spirit Folk Village before Rio went to Strahl Region. They even had a little power contest to see her strength.