Betsuyaku is a boy with black hair. He is usually seen wearing a deer-stalker hat with elongated ear flaps.
When in Trigger Mode, his Border Uniform consists of a shrug jacket with vertical black stripes on the sides of the sleeves and horizontal black stripes around the collar, and matching pants. The jacket is divided in two parts, one for each shoulder/arm, connected by two straps on the front, and by the collar. The jacket also has the unit's emblem in the left chest, and Border's emblem in the shoulders. He also wears a black shirt, mint green pants and brown boots.
Betsuyaku's klutziness tends to irritate Kon, causing her to sometimes scold or even physically punish him. By contrast, it is generally a source of amusement and laughter for Kuruma and Murakami.
Despite his apparent shortcomings, Betsuyaku is a caring, well-intentioned person, and he always apologizes when his clumsiness causes problems. His positivity at all times is infectious and energizes his teammates.
Amusingly, Betsuyaku's clumsiness carries over to the battlefield. He is frequently seen off-balance during combat, and has a notable tendency to fall over awkwardly. Betsuyaku is also occasionally reckless when it comes to firing his weapon. For example, he decided to shoot at Rei Nasu without discretion on the basis that she "probably" couldn't see him in the rain. This penchant for getting carried away sometimes puts him in danger.
Despite Betsuyaku's clumsy nature, he has been shown to be surprisingly perceptive in battle. During Round 3 of the B-Rank Rank Battles, for example, he immediately noticed that Nasu's bullets had become slightly slower than before, indicating that she had switched to composite bullets (Tomahawk) for the first time in the match. In a rare moment of clarity and decisiveness, he pushed Kuruma out of the way, sacrificing himself to keep his captain alive. Kei Tachikawa noted that Nasu's deceptive trump card was something that "many of us would fall for", implying that Betsuyaku's perceptiveness in this situation was somewhat exceptional.
- (About Arafune) "Well, Kō-san surpassed him in an instant. Maybe he felt the difference in their ability?" 
- (To Yuka Kon about Rei Nasu) "It's fine, Kon-senpai. She can't see me, either, in this rain! I think..." 
- "Taichi" (太一? ) literally means "thick one", possibly referring to his dense nature.
- "Betsuyaku" (別役? ) means "different role".
- He likes Neopolitan pasta, tomato-based foods, and making dioramas.