Hiyori initially had a purely business-like relationship with Yato, with him promising to grant her wish to become fully human. This was stalled for a while due to Yato's other priorities and not knowing how to remove her ability at the time. During this, Hiyori and Yato have grown to be very close friends and trust each other deeply. She often acts as the more mature of the two, though both have strange quirks and get along. She also encourages his dreams, whatever serious or childish.
In Chapter 79, Hiyori admitted to having fallen in love with Yato.
Yukine is one of Hiyori's closest friends, thinking of him as a trustworthy younger brother. When she heard about Yato killing a Shinki, she was very worried about Yukine, which was visible when she asked him to accompany her at her house due to believing that Yato was incapable of looking after him. She also cares deeply for him, especially when Yukine told her that he wanted to study, which she encouraged by giving him all of her old school books and occasionally helping him to study.
At first, Yukine only saw Hiyori as a person who he could use until she played a big role in his ablution, giving him words of encouragement that stopped him from turning into an Ayakashi. Yukine is deeply grateful to her for this, becoming very good friends with her. Yukine started viewing her as a closer and more important person to him, worrying about her well-being since she is very important to him and Yato. Yukine sometimes seems worried that someday, Hiyori will forget about him and Yato - which she almost did once if it wasn't for his smell.
Kofuku and Hiyori are on good terms, as Kofuku affectionately teases and calls her "Hiyorin". Hiyori can be a little cautious of her since she is a God of Poverty, but Hiyori cares for her. Kofuku (and Daikoku) were the ones who Hiyori goes to when Yato is in danger, which means that she deeply trusts Kofuku. Kofuku sometimes teases Hiyori about her relationship with Yato.
Yama and Ami are Hiyori's closest human friends. The three are like a group and they are very supportive of each other. When Hiyori gets her "snooze attacks" (leaving her body), they tend to take care of her and don't seem to mind, because it is normal for Hiyori. Hiyori also cares for her friends a lot.
As of Chapter 78, Kazuma seems to understand how Hiyori feels about Yato, but he tells Hiyori that gods couldn't love mortals as it was known to be a sin.