On the surface, Tachihara is an arrogant, impulsive, rash individual, more than willing to solve problems through sheer brute force and his dual guns. A violent temper leads to frequent conflict between him and other mafiosi, namely Gin, whom Tachihara views as creepy and frequently insults, leading to arguments, and Hirotsu, who often shuts Tachihara's temper down by threatening him. Tachihara's self-preservation prompts him to obey Hirotsu in the end, albeit reluctantly.

An apparent thirst for battle and arrogance fuels Tachihara's temper. He's often seen with a rather feral smile on his face whenever fighting. He seldom considers the weight of a mission over the rush of eliminating his targets. He shows no hesitation nor remorse in murder, in fact sometimes urging to just eliminate a troublesome person if he finds their baggage more than they're worth.

A prideful man, Tachihara despises being underestimated and belittled. This is a surefire way to get oneself shot. Despite his rough exterior, Tachihara is capable of thinking rationally, just not in the heat of the moment in the Port Mafia. He can recognize danger quickly.

Ability: He has the ability Midwinter Memento (真ま冬ふゆのかたみ, Mafuyu no Katami) which grants him ferrokinesis, the ability to manipulate metal. It allows Tachihara to remotely control any metal object, mainly his Hunting Dogs blade and his guns. His prowess can even move a mannequin-like a human, and the weapons he controls all float. It has also been mentioned by Teruko that his Ability is useful for stealing, altering information, and also for assassination, which makes him someone who is "born to be a spy".

As a Hunting Dog, Tachihara underwent intensive training and experimentation, making him physically stronger and more durable than an average human and Ability user, however unlike his fellow Hunting Dogs, he is unable to withstand or counter strong attacks (e.g. jet plane), because he had a weaker version of the strengthening surgery due to his status as a spy.

After his battle against Fukuchi of the Hunting Dogs, he becomes severely injured, losing his eyesight due to a slash from a sword.