|Nickname(s)|| Shorty (by Hiiro Okamura)
Cutie Flower, My Angel
|Eye Color||Sky Blue|
|Relatives|| Arnold Ocean|
Silver Dragon Tribe (Ginryuu)
|Binding||Lightning Fang | Thunder Formation Vacuum Attack | Thunderclap Inversion | Silver Lightning of a Thousand Ends|
|Title(s)||Friend of Lightning | Kidnapped | My Angel | Cutie Flower | Girl of Tolerance | Earnest Child | Bothersome One | Good at Getting By | Veiled Girl | Little Girl | A Changing Maiden | Shocking Lolita | Blade of the Wild | Monster Slayer | Killer of the Unique | One Who Endured Hell|
|Accessory||Bracelet of Lightning|
Muir Castrea is the foster daughter of Arnold Ocean and was one of Hiiro Okamura's first traveling companions. She went from admiring Hiiro like a big brother to developing much deeper feelings.
She is a 12 year old girl. With silver hair that reached till her waist, she wears a woolen hat that conceals her hair. Her big eyes have clear sky-blue pupils.
She has vowed to get stronger. But she is unable to believe in herself. She spent her days doubting whether or not she will even be able to influence her own life. To her, fighting is scary and being protected makes her feel relieved. But still, there are people she believes in.
Whether it was good times or bad times, Muir is still honest with herself. She is trying to be true to herself. She has the will to be honest with herself.
She once had a fear of the Humas but her friendship with Hiiro seems to have helped her get over it.
After training with Rarashik, she seems to have gained much more confidence and power. She had also shown herself to be very good at analyzing her opponent's abilities.
Something tragic happened to her home village and it is implied the Humas were responsible. She still find it very difficult to speak about. Her father wound up entrusting her into Arnold's care.
After arriving in Pasion she trained hard for 6 months to get stronger. She showed her improvement by participating the the duel between races with Arnold and her master.
Arnold Ocean - The person who adopted her and is always looking out for her. He seems to be a good parent but sometimes the way he acts around her is very creepy. At first he seemed angry about her feelings for Hiiro, He picked up an unfortunate habit of teasing the girls about it, which got him into trouble.
Hiiro Okamura - At first she uncomfortable around him but grew to trust and rely on him like her Uncle. They were among the few to know of his power early on. She was rather flattered when he took on an appearance like hers and he began passing himself off as her brother. Their relationship at that time seemed very much like siblings. It was only after they were separated for a long time that she began to understand her true feelings. She was pleased when he recognized her growth when they met again at the duel. Like Mimir he worries her unique traits could make her a target.
Winkah Jio - A friend they met early in their journey. It was rare for her to meet people who did not reject her for being half-Gabrabth. She was searching for her missing father. So while they were together for a while they had different goals and split up. But she often prayed for her success and later heart goon news about it.
Rarashik Fan’naru - The person who mentored both her and Arnold. Hiiro helped her to pass the test to gain her approval. It was through her they got a chance to show their skills at the duel Though they were criticized by her for their lack o adequate teamwork and success.
Kuclear King - She was the first member of the royal family they met. She seems to have become good friends with her too. They were both suggested as potential brides for Hiiro by the king. Kuclear found this particularly strange as she hadn't even met Hiiro in person yet.,
Mimir King - Muir was very uncomfortable chatting casually with a princess at first. But over the next few months they seem to have become the best of friends. Mimir recognized Muir as a romantic rival at once. Even though Muir still hadn't realized she felt that way about Hiiro until then.
Leowald King - The king, who they became acquainted with through his daughters. Once they learned of his interest in Hiiro, Arnold decided to blab a bunch of secrets. Muir felt no sympathy when Hiiro punished him for that. He also insisted on testing them when it was suggested they should join the duel between races. Muir turned red when he suggeted Hiiro become a husband to all the girls.
Eonis Kitfal - Her opponent in the duel, who admitted to underestimating her in the fight. Though Muir did not quite win, Eonis stopped fighting when she lost the mask covering the horrible burn on her face. Muir decided to become her friend and got Hiiro to remove the scar for the price of a free meal.
Tenn - Hiiro's contracted spirit who befriended the girls when they visited Pasion.
Muir has awakened to her Binding, by exchanging a contract with the Spirit of Lightjning.
In order to train her to the level of holding her own as an adventurer, Muir, alongside Arnold, are to train for six months under Rarashik. Fortunately her level is already decent, so she is to learn basic combat training, Binding, and practical techniques.
Muir’s silver-grey ears start to glow with a silver light, transforming from ears that would be considered normal to a shape that resembles wings. The size of the ears has also double when compared to the original.
Muir gathers light at the base of her feet. In that moment, her ears flutters as if they are wings. From her current position, as if she were a spring, she kicks at the ground.