Yūichi Jin/Relationships

Mother
Jin's relationship with his mother is unknown, but she was his only known parent before her death.

Sōichi Mogami
Their relationship is unknown, but it's likely Jin cared a lot for his master, as he defeated anyone in his way for Fūjin's ownership.

Takumi Rindō
As Jin's superior officer in the Tamakoma Branch, Rindō has Jin's respect and loyalty, with the latter referring to him as "boss". This is helped in no small part by the fact their beliefs and methods are in complete agreement, seen in how Rindō understood without being told how Jin wanted to approach Yūma during the Black Trigger Capture Arc and gave him the necessary order to do, even though he knew it would put him at odds with the rest of Border's Upper Echelons.

Osamu Mikumo
Jin holds a lot of respect for Osamu as they share the same ideals regarding the treatment of Neighbors, one that is common in the Tamakoma Branch. Jin has saved Osamu on a number of occasions even before the latter joined Border, and was even the one who helped him get enlisted. Jin has referred to Osamu as "Four Eyes" from the day they met, and in spite of his offhand demeanor, he cares deeply for his subordinate, manipulating many events during Aftokrator's Invasion to ensure Osamu's fate (which he saw with his Side Effect) was more favorable. As a result, he deeply blames himself for Osamu's wounds and Replica's fate, promising to aid Tamakoma Second in some shape or form in the future as compensation.

When confronted with his team's shortcomings, Osamu's first course of action was to try and recruit Jin. Although Jin refused due to his pre-existing commitments to Border, he admitted to Sōya Kazama that the idea of following Osamu's orders "sounded fun".

Yūma Kuga
Jin views Yūma as his junior and sees his younger self in him. As such, he wants him to have fun in Border, even giving up his Black Trigger, Fūjin, in order for Yūma to be enlisted. Jin would later claim he has no ulterior motives other than wanting to "act cool" and support Yūma and his team.

Replica
Jin respected Replica, calling him "sensei" (先生), a title reserved for teachers, out of consideration for the vast amounts of knowledge Replica brought with him. Jin blames himself for Replica's abduction during Aftokrator's Invasion, and has promised to make it up to Osamu and the rest of Tamakoma Second.

Chika Amatori
Not much is seen of their relationship as they rarely interact, but Jin has demonstrated good will towards Chika, pulling strings to ensure her team's success and making a coordinated effort to ensure her safety during Aftokrator's Invasion. However, Jin was not above using Chika as bait to reduce collateral damage during the invasion, although he regretted having to do so. Chika, on the other hand, is somewhat shy around Jin due to his outgoing tendencies.

Kyōsuke Karasuma
Jin and Karasuma have both been a part of Border and the Tamakoma Branch for a long time. As such, they share the same values and morals, with Karasuma viewing Jin as his senior. Jin acknowledges Karasuma's strength, to the point he even left him in charge of taking care of Mikumo and the other C-Rank agents during the Second Large-Scale Invasion while knowing they would be closely targeted by Aftokrator. In the anime, Jin's compliment and reassurance on the impact of Karasuma's efforts against Hyrein were able to alleviate the former's frustration over his defeat.

Reiji Kizaki
As a fellow member of the Tamakoma Branch, Kizaki gets along well with Jin, and is his primary confidante regarding his plans for the future, a topic they regularly discuss over ramen, as pointed out by Karasuma. Jin respects Kizaki and holds his strength in high regard, knowing his strong suits in combat and entrusting him with the highly crucial task of delaying Hyuse and Viza during Aftokrator's Invasion, a task that Kizaki took extremely seriously.

Kirie Konami
Like Karasuma, Jin often takes advantage of Konami's gullible nature to mislead her, but they get along well enough both on and off the job. Konami treats and addresses Jin as an equal in spite of his advanced age, and is well aware of Jin's propensity for dealing behind the scenes and "pulling strings". In the build up to Galopoula's Invasion, Jin reminded Konami that their efforts would directly impact Tamakoma Second's ability to advance in the Rank Wars, a matter both of them took special interest in.

Shiori Usami
As fellow members of the Tamakoma Branch, Jin is on friendly terms with Usami, and the two often bounce off each other. Jin also seems to rely on her to a degree, as he entrusted her with educating the new recruits for Tamakoma Second about Border protocol and triggers.

Yōtarō Rindō
As a permanent resident of the Tamakoma Branch, Jin often keeps Yōtarō company at home. Unlike most of the other members, who treat Yōtarō like a child, Jin seems to have more faith in the boy's maturity, as he was willing to leave both the powerful and dangerous enhanced trigger, Lampyris, and the matter of their prisoner of war, Hyuse, to Yōtarō's discretion. Jin was also highly concerned for Yōtarō's safety during Galopoula's Invasion, dropping all his other commitments to rush to his side. Later, Jin and Takumi Rindō took Yōtarō along with them when they approached Ratarykov and Reghindetz for important negotiations in spite of his young age.

Kei Tachikawa
Jin and Tachikawa are battle rivals. They are constantly at odds with each other, but taunt and admire the other during their battles. According to Shūji Miwa, there are uncanny similarities in the way the two rivals exploit loopholes to get what they want. In spite of being in opposing factions within Border, they have no problem socializing, and are quite friendly around each other outside the job.

During the skirmish over Yūma's Black Trigger, both combatants joyfully reminisced over the opportunity to fight again. Upon Jin giving up his Black Trigger (and thus his S-Rank status), Tachikawa felt euphoric over the chance to duel him again, and Jin has made it his objective to take Tachikawa's position as the no. 1 Attacker, demonstrating the mutual reciprocation of their rivalry.

Shūji Miwa
Despite what Miwa thinks of Jin, Jin seems to like him a lot, calling him by his first name and even offering the Fūjin to Miwa if he saved Osamu. For his part, Miwa has grown more accepting of Jin as well, reminding him to do his job before Galopoula's Invasion, and agreeing to cooperate with Jin to defeat Koskero on his operator's advice.

Sōya Kazama
Like Tachikawa, Kazama has no issue interacting casually with Jin outside the job. This was best seen in how Kazama and Tachikawa approached Jin mere hours after losing to him during the Black Trigger Capture Arc, and chatted amicably while sharing rice crackers. Although Kazama has stated he finds Jin annoying, they still converse freely on a number of occasions, particularly about Osamu, since both are invested in his growth. Jin seems to think highly of Kazama's combat abilities, as he hoped Kazama would target Arashiyama Squad instead of him during the Capture Arc, and was willing to entrust the safety of the Expedition Ship to Kazama and the other top Attackers during Galopoula's Invasion.

Jun Arashiyama
Jin and Arashiyama are on largely friendly terms, which allowed them to quickly and effectively work together against the Kido faction during the Black Trigger Capture Arc. Arashiyama appears to have great faith in Jin's capabilities, as he let the latter take on the brunt of Border's Top Teams, and later remarked that Jin "makes good on his word" upon the S-Rank agent's triumph over Tachikawa and Kazama Squads. Ashihara has noted that the two share hairstyles.

Shun Midorikawa
Jin is quite friendly with Midorikawa in general, and will occasionally take up his requests for Rank Battles, much to the younger Attacker's jubiliation. Jin's involvement in having Yōsuke Yoneya, Kōhei Izumi and Midorikawa support Osamu and the C-Ranks during Aftokrator's Invasion piqued Midorikawa's interest, and perhaps even motivated him.