|“||Feelings have nothing to do with strength. Power, strategy, and luck are what decide a battle.||”|
Kei Tachikawa (太刀川 慶 Tachikawa Kei? ) is a character in the manga and anime series World Trigger, the A-class leader of Tachikawa Unit and both the number 1 Attacker in Border and the number 1 agent overall. Due to his actions, he was an antagonist of the Black Trigger Capture Arc, but later becomes a supporting character.
Tachikawa has medium length, wavy brown hair (gray in anime). His brown (gray in anime) eyes have an odd crosshatched design.
In trigger mode he wears a black trench coat, adorned with red pinstripes. The unit emblem takes place on his shoulders. He also wears black pants and black boots.
Tachikawa is an arrogant person and as a result he's carelessness, risk-taking and underestimating the enemy are his flaws. Also, he tends to be in his mind a lot, and becomes anxious when an opponent is surprisingly more difficult. But by being in his mind he analyses the the situation with the information that he acquires in in battle.
He also acts like Jin, they have a similar way of thinking, which makes him unliked by Miwa. Despite that, he's quite friendly outside of the battlefield. He likes to joke around, just like Jin. He has strong views of strength, seeing it as a product of strategy and strength. But unlike Jin, Tachikawa is very dedicated in ending a battle quickly and perfectly. Similar to a samurai he keeps a firm posture, and a habitual technique to persistently execute devastating blows. He can be seen as aggressive when fighting, due to the destruction of city property and sacrifice of a squad member. Moreover, being blind due to his focus, he is unable to have a larger viewpoint of the situation and turn the battle into his favor.
However, this is good for 1v1s, because of his habit to lock onto an enemy. In summary, when Kei Tachikawa wears his trion suit, and wields his Kogetsus, resilient, powerful, precise, attentive, disciplined, logical, humorous, selective, observant, helpful, confident, reliable, and controlled are a few words that describe his personality. He is harsh towards Murakami, possibly because he has high expectations for the prodigy.
Sometimes, he might come off as insensitive, such as saying that feelings don't matter in battle as he would never be the number 1 in Border if that was the case. However, he later corrects himself by saying that he does like battles with emotion, but feels attributing the results to emotions is like saying the loser didn't want enough to win.
Kei and Yūichi have a similiar way of thinking, so they understand each other. Tachikawa thinks of Jin as a rival and looks forward to fighting with him to see who is the best attacker in Border. When they're not fighting he is quite friendly towards Jin.
Miwa dislikes Tachikawa, because he is similar to Jin. Tachikawa, on the other hand, seems to not notice it and appears to like Miwa. Tachikawa also likes to tease Miwa.
Mutual respect, although Kazama is one rank below. Both appreciate rice crackers and coffee, Kazama doesn't appreciate Tachikawa's attitude at times towards battle.
Tachikawa and Konami have a relationship of mutual respect and friendly rivalry. Despite being both top attackers in Border, respectively, they refuse to acknowledge either of them as superior to the other. As shown during Galopoula's invasion, however, Konami is annoyed by Tachikawa's careless and playful personality.
- (To Yūichi Jin) "3 weeks until official enlistment day. During that time, I'll definitely defeat you, and recover the Black Trigger." 
- (During Aftokrator's invasion.) "Right, right. Let's finish this before lunch." 
- (During Tamakoma Second's second Rank Battle) "Feelings have nothing to do with strength. Power, strategy, and luck are what decide a battle." 
- (Ditto) "Don't get me wrong, I love battles with emotion. But, if you attribute the result of the battle to emotions, you could as well say the loser just didn't want enough." 
- (About Suzunari First) "Murakami and Taichi would come to protect Kuruma no matter what. That's how Suzunari First fights as a unit." 
- (About Osamu Mikumo) "Mikumo's aim from the very start was to deplete Nasu's trion. On top of having Amatori escape to reduce the risk of being destroyed, he went in for another point. Now I see. He's really a ruthless guy." 
- (To Takeru Yuiga) "Alright, listen. I'm gonna say something good. Look at our emblem. There are three swords, right? This first one is me, the second one represents Izumi, and the last one is... My second sword. In other words, you're still a novice, so no getting puffed up. [...] Kunichika, you're the crescent moon on the back." 
- "Kei" (慶) means "to congratulate, to celebrate".
- "Tachikawa" (太刀川) means "Tachi River".
- He likes Udon, Mochi (Japanese rice cake), croquettes and winning in Ranks Battles.
- According to Ashihara's Q&A, he has done a lot of stupid things outside of battle:
- Hes read the word "Danger" [deyn-jer] as "Dangah".
- He once thought a computer was broken when it was just unplugged.
- He only ate the dried fruit on a fruit granola bar.
- When asked in a Q&A if the reason why Tachikawa's eyes resemble a grid is because "he burned the mesh for grilling his beloved mochi into his eyes", Ashihara said that's probably the reason.