As Yamato considers connections and friendships important, he has several relationships with various people and peers around him. Either in just inside the Kawakami area or just his Kazama Family members, including the rivals from the Itagaki Siblings as well. This
KAZAMA FAMILY
The Kazama Family, Yamato's band of friends which live together from childhood and as one of the founders along Kazama Shouichi. Of the group, he is nicknamed "gunshi" (tactician) for him always using his brain, planning things out first mentally just like one.
KAWAKAMI MOMOYO
Momoyo is a childhood friend of Yamato. In their early days, he accepts Momoyo's request to be her brother and is constantly teased by her whenever she's bored. Yamato holds a great deal of respect for Momoyo's fighting prowess, but will sometimes be concerned about her getting too stressed if she has a lack of strong enemies to fight and test herself. Likewise, Momoyo will sometimes be concerned for Yamato's well-being due to his general lack of fighting strength, holding a lot of affection for her adoptive sibling. According to Momoyo, 'observing' him has become one of her hobbies since the day Yamato accepted the offer be her brother. The two compliment each-others strengths - Momoyo holds the combat power while Yamato has the intellect. She also hits him up for money often, but he will usually oblige her as she always pays him back in the end.
KAWAKAMI KAZUKO
Like the rest of the Kazama Family, she is treated like a dog by Yamato. His relationship with her is similar to one like an owner and pet - except Yamato was the one who trained her so thoroughly that she would react to certain actions that a dog would normally react to as well, such as a dog whistle. He takes care of Kazuko as if he owned an actual dog, rewarding her with delicious food or petting her head when she does something good, and when she does something bad she is punished (usually mentally, and rarely physically).
SHIINA MIYAKO
Because Yamato sat next to her throughout elementary school, saved Miyako (with the help of Kazama Shouichi) from the bullying that stemmed from being hated by her classmates and perhaps the whole school because of her mother's affair, and was her first friend she had, he brought her to life. In bringing her into the Kazama Family and thus, giving her even more friends than she could ever hope for in her life, she fell in love with him as a result. However, Yamato tends to reject her advances, seeing them as family more than a romantic couple.
Christiane Friedrich
Due to their conflicting ideologies - Chris' strong sense of justice, and Yamato's preference for subterfuge and underhanded tactics - the two butt heads with each-other often. Yamato will also often use Chris' outdated idea of Japanese culture to tease or embarrass her. However, in spite of being "natural enemies" due to their vastly differing methods, or the conflicts that arise from Yamato's practical jokes, none of their bickering on morality or practical necessity ever causes lasting resentment between the two. Plus when Yamato goes to the bath he mostly encounters Chris naked or partially furthering their conflicts, even Chris has gotten used to this to the point where she'd even warn him that she was already there.
Mayuzumi Yukie
Yamato's more easygoing personality is a stark contrast to Yukie's shy, introverted one, and he admittedly finds her personality quirks to be a bit strange. But nevertheless, he and the rest of the Kazama family tend to enjoy her soft-spoken nature, as it serves as a nice contrast to the typical wild, impulsive and unpredictable nature natures of Momoyo, Kazuko, and to a lesser extent, Shouichi.
Kazama Shouichi
One of his best friends, Yamato holds a great deal of respect for the "Cap" and head of the Kazama family, and to a lesser extent, some envy for him. While Yamato can outmaneuver Shouichi in terms of tactics, Yamato feels that Shouichi has him beat when it comes to "being cool," and has vowed to someday beat Shouichi at being a man or being cool at something. Though, this doesn't cause any true bitterness, and is mostly out of how much he respects Shouichi's boundless charisma and energy. Likewise, Shouichi holds great respect for Yamato's tactical ability and observational skills.
Shimazu Gakuto
One of the first members alongside Takuya to join the circle of friends that would eventually be the Kazama Family, Gakuto and Yamato are good friends, despite the former's jealousy with how Yamato - and Shouichi - can make girls fall for them so relatively easily. He and Yamato share a trait in that they are both rather perverted, though unlike Gakuto, Yamato doesn't openly advertize it, and the two of them, along with Takuya, share a secret stash of porn magazines that is hidden in the Kazama Family base, which they all think is a secret from the girls.
Morooka Takuya
The 'geek' and 'otaku' of the Kazama Family, and the fifth member to join it, Moro shares a good friendship with Yamato, with their very first interactions with each-other having been to apologize for the reckless behaviors of their respective friends - Gakuto and Shouichi respectively. Like Yamato, he prefers to avoid direct confrontations, so he often assists Yamato in his plans and strategies, and is one of the few people that Yamato confides with his plans and methods. This is true even in the Kazama family, as Gakuto, Shouichi and Kazuko lack the understanding, Momoyo and Minamoto lack the motivation (unless bribery is involved, in Momoyo's case), Yukie lacks the courage, Chris lacks the desire to help with "dirty tactics," and Miyako would only use the assistance as leverage to try and force a date.
Tadakatsu Minamoto
An acquaintance of the Kazama Family (later the group's tenth member in the Agave storyline of Majikoi), and childhood friend of Kazuko, Tadakatsu and Yamato have what could be described as a cordial relationship, more along the lines of roommates or neighbors then friends, but that is mostly due to Tadakatsu's typically standoffish personality. Yamato is able to recognize Tadakatsu has a kind nature, though sometimes takes advantage of it to get him to cook the groups meals, much the same as Shouichi does. But it never causes any grudges between them, in spite of Tadakatsu's outward attitude, since Tadakatsu forgives and forgets easily.
2-F CLASS
He has a good reputation with most of the class, because he is respectable most of the time to the staff and the students in the school, because they are all acquaintances. He fairly gets along with the women and more with the men.
2-S CLASS
Unlike his reputation with 2-F, he is ridiculed by 2-S for being in class 2-F, who Kokoro Fushikawa calls, "A bunch of monkeys". However, he is respected by some students, such as Aoi Touma for rivaling his intellect and wits. He also has a strong friendship with the Bushido clones, especially Benkei Musashibou, who is part of the Lazy Club with him and Class 2-S teacher, Kyojin Usami. And also Yoichi Nasu, due to Yamato being a chuunibyou like him at one time.
Aoi Touma
Musashibou Benkei
In the visual novel, Benkei and Yamato became close in different situations, mostly in her route, they were in the Lazy Club where they developed a bond which turns into a relationship.
Yoichi
ITAGAKI SIBLINGS
The Itagaki Siblings have a strong rivalry with the Kazama Family due their different goals as well as opposite motives, including love rivalries (especially Tatsuko with Momoyo and Miyako).
Itagaki Tatsuko
Tatsuko met Yamato when he was taking a nap near a river. Having the tendency to be sleepy, she decided to nap next to him. After then she developed a crush on him when she notices he's cute in her perspective. She is straightfoward and admits that Yamato is cute. This soon turn into their normal routine every-time Yamato takes a nap in the same spot. In Benkei's route, when it is their turn to fight. Instead of fighting him seriously. She actually simply give him a big hug. Much to her joy.