- " Those guys [the Elemelians] are going after Twin Tails. I can't just stand by and watch . . . . "
- Sōji Mitsuka (観束 総二 Mitsuka Sōji?) /
- Tail Red(テイルレッド Teiru Reddo?)
- Voiced by: Nobunaga Shimazaki (Japanese); Austin Tindle (English) / Tail Red Voiced by: Sumire Uesaka (Japanese); Bryn Apprill (English)
Soji Mitsuka is a typical teenage male, slightly tall, with an average build body that is slightly muscular. He is most often seen wearing his high school uniform, that looks like a business man's suit. Soji has reddish maroon hair that is styled in a Beatles cut, and at times his hair looks somewhat unkempt. His face is a bit angleir, with a pointed chin. He has a girl's 'big eyes', but with a more oval shape to them, and has auburn crystal eye color. Soji's skin tone is medium-to-tan beige, and has the same evenness about it so as to look very attractive.
Soji's school uniform business suit consists of a white dress shirt, with a powder blue tie. Worn over that is a medium to dark beige business jacket with black velvet trim, and black dress pants with a powder blue stripe down the side. He wears black oxford shoes. For casual wear, just a T-shirt and casual pants will do. In cooler weather, he will wear a light jacket over the T-shirt.
The main protagonist is a normally gentle-natured male, a 15-year-old freshman of Yōgetsu Private Academy, who is absolutely obsessed with girls who wear the twintail hairstyle. He even requests the school to form a " Twin Tails Admirers " Club. Soji is a loner, who has only one close friend, a teenage girl named Aika, who has been his constant companion and playmate since they were little children. She treats Sōji like a little brother and is rather over protective of him, although this is later discovered to be because of her massive crush that she has developed on him sometime after puberty.One day, he encounters a mysterious beautiful young woman named Twoerle, who appears before him after coming from a parallel universe. At the same time, monsters, called Elemelians, begin to appear in his town, and they start attacking the citizens, mostly teenage girls who wear their hair style as twin tails. Normally, Soji does not get much excited about anything, willing to 'go with the flow' when trouble appears. But in a situation where girls with twin tails are losing their desire to wear twin tails, Soji becomes incensed, and immediately jumps into action without a second thought. In the midst of the chaos, Twoerle entrusts Soji with 'attribute power', and a battle maiden outfit called, " Tail Gear ", thus suddenly transforming him from a teenage boy, into an adolescent twin tail Warrior Girl, known as Tail Red. And although slightly slow to understand situations, they find that 'when push comes to shove', that they can think and learn quickly, and react to changing situation in the 'blink of an eye'.
Soji appears to be a Bigender ( * ) character, becomes comfortable with that fact, and after a while does not seem overly concerned that they can, by means of a Henshin, transition between male and female genders. Later in the series, Soji transitions to a teenage female, without her Tail Gear, and becomes an ordinary female teenager who takes the name Solar.
- (*) Bigender, bi-gender or dual gender is a gender identity that includes any two gender identities and behaviors. Some bigender individuals express two distinct personas, which may be feminine, masculine, or other gender identities; others find that they identify as two genders simultaneously. Identifying as bigender is typically understood to mean that one identifies as both male and female or moves between a masculine gender expression and a feminine gender expression with little or no middle ground, or both.