Soubu High School Edit
Zaimokuza gets along fine with the service club and thus becomes an unofficial member. He sometimes helps the Service Club with requests, usually because he likes being included, no matter the activity.
He and Hachiman were often paired together for gym class as first years, They were always the last 2 people without a partner because they are both loners. They are good friends, although both deny it.
Zaimokuza refers to Hachiman as his partner or underling when involving him in his Chuunibyou delusions. Zaimokuza trusts Hachiman enough to share with him his ambitions of becoming a light novel writer, and Hachiman cares enough to help him out by giving him harsh and critical, yet meaningful, feedback.
Zaimokuza gave Hachiman a list of places to search Sagami when she hid during the Cultural Festival. Hachiman trusts Zaimokuza's creative talent, as he recommended him along with Ebina to the Athletic Festival committee to make the special events interesting. Hachiman cares enough to notice when Zaimokuza is left out of a group (Summer Camp Arc, Yui's birthday invitations, etc.).
Zaimokuza also cares for Hachiman. He was willing to hear his concerns when Yukino and Yui decides to run for student council. He offered to help Hachiman create a fake online support group for Iroha, even though he did not like doing so. He also attempted to block others during the student marathon, so Hachiman could have a private conversation with Hayama.
Yukino doesn't seem to be bothered by his presence, preferring to completely ignore and avoid him in most cases. Yukino however did offer to cure his Chuunibyou syndrome, which she sees as a mental issue the very first time she met him. Despite Yukino's reluctance to acknowledge him, she does offer her assistance when even he has a request.
Zaimokuza on the other hand is unable to communicate well with girls and tries to avoid any conversation with Yukino. He considers her so honest it's hurtful.
Yui nicknamed him Chunni. She is sometimes polite to him and considers him Hachiman's friend. However, she always gives him a disgusted or confused due to his eccentric personality, or when his Chuunibyou Syndrome acts up.
Yui initially wasn't going to invite him to her birthday party until running into him by chance. She was unable to turn him away and invited him afterwards.
Zaimokuza initially thought Totsuka was a girl until learning the truth. Zaimokuza sometimes has lewd thoughts about him and even tried to get him to wear a maid outfit.
Zaimokuza usuall hangs out with Totsuka when Hachiman is around. He accompanied them to the arcade and to the theater. Totsuka gave Zaimokusa a picture of them. Totsuka considers himself to be a friend of Zaimokuza's, stating "a friend of Hachiman's is my friend as well". Totsuka also said that he is jealous of closeness between Hachiman and Zaimokuza.
Totsuka might be the only person not put off by Zaimokuza and most likely sees him as real friend.
She formed a creative partnership with Yoshiteru, during the Athletic Festival. They showed a lot of similarities and eccentricities when it comes to manga and anime references.
They worked very well together for the festival but were not mentioned to hang out or talk afterwards.
Zaimokuza feels intimidated and hurt by the presence of Hayama, who is much more charming and popular than he is. However he continuously finds himself being charmed by Hayama and personally harbours no ill will towards him. He still enjoys seeing Hayama fail at things (Taishi's request), and took pleasure in knocking down the white teams pole during the Athletic Festival.
Hayama remembers Zaimokuza well, during their first meeting he was able to recall his name correctly. During the Judo tournament, Hayama recommended Zaimokuza to be a member for their team.