Kei Tachikawa/Relationships

Yūichi Jin
Tachikawa and Jin 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.

Kōhei Izumi
He thinks very highly of Izumi, as they are teammates and friends. Tachikawa mentions that the second blade on their Squad emblem represents Izumi, while the other two are himself and his second blade.

Takeru Yuiga
Despite the two being in the same Squad, Tachikawa thinks very lowly of Yuiga due to how he got his position in Tachikawa's team. The bias is so bad that Tachikawa put his second Kogetsu blade in the Squad's emblem before Yuiga himself.

Shūji Miwa
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.

Sōya Kazama
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.

Kirie Konami
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.

Ren Tsukimi
According to Daisuke Ashihara, Tsukimi is Tachikawa's childhood friend.