Although I look like this, I'm actually a respectable teacher!
Bimii (ビミィ Bimii, real name △×○□◇) is the teaching staff at Mikagura Academy as well as Eruna's companion. In the fifth novel, he turned back into his normal human form.
Bimii is a living being who takes the form of a cat. He has small wings which help him fly. The color of his fur is white with brown on the tails, feet, and face. He also wears a flower choker on his neck and is said to be ikebo (slang for iketeru-boisu/cool male voice). He also attaches '~ryui' to the end of his words. However, his anime counterpart has purple eyes and tail. His wings are also slightly yellowish and his fur is slightly darker.
In the fifth novel, he returned to his normal self which is a human. He looks like a middle-school-aged boy who has pale pink messy hair and is almost always chewing pink bubblegum. He wears a black jacket with pink hoodie and white shirt underneath, black pants, and a white armband with the Mikagura Academy emblem on it on his left arm. He also wears a pink and white headband, a pink choker, a pink-white striped tie and beige shoes with a matching pattern. Aside from this, he also brings a backpack anywhere with flowers and something that resembles his tail in his cat form as an accessory.
Bimii is a flying cat who has always accompanied Eruna from the moment she was accepted in the Academy. Although he did properly introduce himself to Eruna, Eruna didn't manage to hear his real name so she decided to nickname him Bimii instead, from his bimyou (lit. questionable) appearance. He is also the teaching staff of Mikagura Academy, as many of the students recognize and call him as Sensei. However, unlike Kurumi he's never seen teaching students and it seems his duty is to follow a single unique student in eachyear or act as the referee during battles. He also seems to know the particular traits of each student quite well and get along well with them. An example is when he told Eruna about Kyoma's past. Though Kyoma and himself aren't best friends nor enemies (for a certian incident from Kyoma's past), but at least respect each other.
Bimii is also known to be the victim of Eruna's and later, Otone's pranks and is often amazed by and even comments on their personalities like a straight man. He also sometimes gets tired of Eruna's antics. Despite this, he still accompanies her and helps her in her everyday school life by providing explanations of school systems and is even willing to be the adviser for the club that she will create.
When he is back to his normal form, his personality has slightly changed, as he describes himself as someone whose role depends on his appearance. He also projects an image of a cool guy and uses quite a rough speech pattern, although not as rough as Kyoma's. He also sometimes accidentally slips '~ryui' end words, indicating that he is still not used to his body, much to his frustration. Still, the treatment he receives from Eruna and Otone is as same as ever.
After succeeding in training Seisa to be a special and the strongest person in Mikagura and now currently taking Eruna under his wing, Bimii is indicated to be strong in battle, which is appropriate considering his status as a teacher.
↑The ryuiryui nickname came from Akina's tweet about a fan who asked his real name.
↑According to his tweet, 演じてくださることが決まって「僕、本当にビミィですか……？」と困惑していたそうです！あなたこそがビミィです！！ When he was settled to portray Bimii, he seemed to say it in bewilderment, "Is it really me who become Bimii...?". Sure for that reason, you're Bimii!!