Hayato's family is on good terms with the Yukinoshita's, however, this is not known by many at the school. He, along with Yukino, studied together at an elementary school overseas (the USA in the light novel). His family is wealthier than the Yukinoshitas. It was mentioned that in their younger years, Haruno would look after Hayato and Yukino when their parents were out on business ventures. It was also mentioned that the trio spent time in the amusement park where Haruno would mess with them resulting in a fear of rides for Yukino. During middle school, there were rumours about him and Yukino being a couple that spread throughout the school causing a strain in their friendship.
He took football seriously in middle school and continued in high school. In high school, during the middle of his second year, he was made captain of the team.
Something regarding Rumi's situation bothers him which Yukino confirms. Hayato also told Hachiman that there was an incident similar when he (and Yukino) was younger, but he couldn't do anything about it. He also thinks things would have been different if Hachiman was there.
During the field trip, Hayama told Hachiman that things once lost could not be retrieved as a reference to his past. However, he decided to refrain from speaking about it in detail, with Hachiman choosing to not press the issue.
Hayato is reluctant to take any Valentines chocolate. Yukino once reminisced that back in their elementary school days, this would leave a troubled atmosphere in the classroom the following day.
Hayato choose work tour related to media or a multinational corporation. Hina feels that it was something related to his career path for the future.
During the double date Hayama and Hachiman share their opinion of love. Hayama says aloud that he feels both of them have never truly fallen in love before, causing Hachiman to recall the time at the summer camp where Hayama gave off the initial "Y" for the name of the girl he liked.
In times of winter holidays, both Hayato's and Yukinoshita's families were planning for a new year's feast to which Yukino was relucant to attend. Both Yui and Hachiman went shopping to purchase Yukino's birthday present, coincidentally running into Haruno and Hayato. Haruno uses this opportunity to lure Yukino. Both Yukino and Hayato were witnessed in the cafe by someone from Sobu High which resulted in another rumour of them dating. It spread throughout Sobu High, resulting in a difficult and awkward situation for Hayato and his clique.
This rumour also lead to the confessions of many girls who had a crush on him, creating more tension.