|“||All of the flavor bits fell out and died!!||”|
Betsuyaku is a thin, light-skinned boy with a round face, big eyes, notable eyelashes, especially under his eyes, and medium-long, unkempt black hair over which he is usually seen wearing a brown deer-stalker hat with elongated ear flaps. He appears to like wearing black sweaters with a simple image on the chest, and on one occasion a sweater with dark, horizontal stripes.
Betsuyaku's uniform is nearly identical to his teammates'. It consists of a forest green shrug jacket with vertical black stripes on the sides of the sleeves and horizontal black stripes around the collar. The jacket is split in two parts, covering Betsuyaku's arms, shoulders, and part of his ribcage and back on either side. The two sections are connected by the collar, two thin straps on the front and one on the back. Border's logo is emblazoned at the top of each sleeve. The uniform is completed by a black shirt with one vertical green line running along each side, beige pants and brown boots that reach up almost to Betsuyaku's knees, and an identical hat to the one he wears in his normal body.
Betsuyaku is the archetypal klutz, being extremely clumsy and frequently tactless with his words, not uncommonly as a result of thoughtlessly acting out of excessive eagerness or earnestness. He is a very expressive person, which manifests both in his cheerfulness and his dismay, which is often caused by his own catastrophic actions. For all his clumsiness, he is in fact a caring, well-intentioned person, and he always apologizes for the trouble he makes. Betsuyaku is easily excitable and very optimistic, and his infectious positivity energizes his teammates. The comedy he provides is not exclusively unintentional, and he appears to enjoy making others laugh. He is surprisingly sensitive to criticism, bursting into tears when the strategy he proposed in round 7 did not work as well as it could have, although his mood changed extremely quickly as soon as he was indirectly praised.
Betsuyaku's optimism and clumsiness carry over to the battlefield, frequently leading him to underestimate his opponents and act recklessly. This penchant for getting carried away sometimes puts him in danger. He is quick to worry and even panic; however, he seems to calm down rather just as quickly, especially when he is with someone else, and might have grown more capable of maintaining his cool over time. In addition, he has a notable tendency to fall over awkwardly during combat, and while many of these instances were due to the extreme weather conditions of round 3, there are also cases in which his loss of balance was solely the result of his own actions.
For all the downsides of his personality in combat situations, Betsuyaku has demonstrated a useful ability to think outside the box which, when applicable to strategy, makes his unit's courses of actions very difficult to predict, leaving opponents guessing. He can also be unexpectedly perceptive, immediately noticing that Rei Nasu's bullets had become slightly slower than before, thus saving Tatsuya Kuruma in a rare moment of clarity and decisiveness.
Betsuyaku deeply respects Kuruma, who in turn looks after his very clumsy teammate and routinely forgives him for the accidental havoc he wreaks, including the destruction of his beloved aquarium of tropical fish. It was Kuruma's patience in the face of the loss that earned him Batsuyaku's enduring loyalty. He gifted the Sniper his hat as protection, taking the idea from Yōtarō Rindō's helmet, a thought which Betsuyaku greatly appreciated. Like Murakami, Betsuyaku will not hesitate to put himself at risk to ensure Kuruma's safety no matter the circumstances. The three and Kon hang out together in their free time. Betsuyaku addresses Kuruma by his surname followed by the honorific -senpai, while Kuruma uses the Sniper's first name, without honorifics.
Betsuyaku and Murakami are teammates and friends, and on occasion hang out together with the rest of Suzunari First. Betsuyaku respects Murakami and depends on his strength. For his part, Murakami is very attached to he Sniper, whose clumsiness he finds amusing, and will do everything in his power to protect him. The two are on a first-name basis, though Betsuyaku adds the honorific -san, thus combining informality and respect, while Murakami adds no honorific.
Betsuyaku's klutziness, which his other teammates tolerate or find amusing, tends to irritate Kon, causing her to sometimes scold or even physically punish him. For these reasons, he finds her slightly intimidating. Nonetheless, the two may hang out with their teammates even outside of Border. She calls him by his first name with no honorific, presumably signifying closeness, whereas he addresses her very respectfully, appending the honorific -senpai to her surname.
Betsuyaku and Satori are schoolmates, if not friends, and close enough for Satori to casually put his hand on Betsuyaku's shoulder. The Sniper of Arashiyama Unit finds Betsuyaku's antics during joint Sniper practice hilarious.
Tōma knows Betsuyaku well enough to include him in his list of targets during joint Sniper practice. During the Galopoula blitz, Tōma and Betsuyaku were seen goofing around, with the no. 1 Sniper picking up the severed head of a Dog and having it "bite" Betsuyaku.
While Tachikawa referring to Betsuyaku as "Taichi" in his commentary might be due to him not knowing how to read the kanji of his surname, the lack of an honorific could still suggest that the two are on friendly terms.
Betsuyaku and Inukai appear to be on good terms, as in his commentary Inukai referred to the Sniper by his first name with the honorific -kun. Although the commentary caused him to burst into tears, Betsuyaku seemingly did not hold it against Inukai.
Kageura refers to Betsuyaku by his first name, without honorifics, which could imply that the two are on good terms with each other.
Kitazoe refers to Betsuyaku by his first name followed by the honorific -kun, possibly implying that the two know each other.
Betsuyaku originally assumed that Arafune had quit being an Attacker due to being dwarfed by Murakami's talent, but after listening to his recorded message, he learned the truth and concluded that Arafune was in reality a very kind person. Betsuyaku refers to him by his surname with the honorific -san.
Betsuyaku was profoundly grateful for Arashiyama's positive remarks on his unpredictability. He refers to the A-rank agent by his surname followed by the honorific -san.
- (To his teammates) "All of the flavor bits fell out and died!!"
- (To his teammates) "That's because Kō surpassed him already! Maybe Arafune just realized he has no talent?"
- (To Tatsuya Kuruma) "Compared to the humanoid Neighbors, taking care of Nasu will be a piece of cake!"
- (To Yuka Kon) "It's fine, Kon. She can't see me, either, in this rain! I think..."
- (To Kuruma) "You saved me! Nasu's scaaary!"
- (To his teammates) "We'll move up too! I hope Tamakoma Second loses big!"
- (To his teammates) "We'll be fiiine! Cuz this is their first time up against our new formation!"
- (To his teammates) "We could try poisoning the other squads' Operators? How about that?"
- (To his teammates) "How about I do that thing I've been itching to try!"
- "When the tide turns rough, beat a retreat."
- "Taichi" (太一?) is composed of the kanji for "thick" and "one". "Betsuyaku" (別役?) means "different role".
- Betsuyaku likes Neopolitan pasta, tomato-based foods, and making dioramas.
- Like Arafune and Akane Hiura, Betsuyaku keeps his hat in his trion body to shade his eyes while sniping.
- According to the author, if Betsuyaku were to leave Border, his memories would probably be sealed to prevent leaks of information.