Hiiragi Kashima (鹿島 柊) is a high school student who, along with Mafuyu, seems to know something about Mafuyu’s guitar. He is also Mafuyu's former classmate. He formerly played bass in a band with Yuki and Shizusumi.
He has dyed yellow blonde hair with his fringe parted to the sides and a pair of ear piercings in his left ear. The hair length is short enough to show his ears and Hiiragi wears a white collared shirt untucked into his grey trousers with the top button undone with a loose light green tie with darker green diagonally horizontal stripes running down it. He also wears a darker green blaser with the white ends of the sleeves rolled up to his forearms and a pair of laced boots.
He has a very sweet personality towards others and worries about his friends as well as wanting to encourage them. Hiiragi is also very observant and can often tell from his close friends what their thoughts and feelings are. In fun, he tends to scold people he's conversing with. He can from time to time act flippant.
Hiiragi comes across Mafuyu by chance in the street with Ritsuka. After checking that it is him he happily asks what is he doing here, he has not heard anything from him in so long. Noticing Mafuyu's guitar he recognizes it as Yoshida's and asks Mafuyu if he is playing music now.
Having found his way to Mafuyu’s work at a concert venue, he evidently interacted with Tsubaki where she takes him to Mafuyu. Hiiragi cheerfully greets him and asks to borrow Mafuyu for a while. As Tsubaki walks away he says not to mind him, it is not like he came to blame Mafuyu.
Making their way nearby to a train walkway Hiiragi procures a Black Poss canned drink. He begins immediately, enquiring whether that is Yuki’s guitar. Hearing that his mom told Mafuyu to take it, Hiiragi was aware that both their parents pretty much acknowledged their relationship. Asking whether Mafuyu has seen someone called Saeko, he states when he told her Mafuyu had started playing music she was really happy.
He has been wondering, if Mafuyu started music because he decided to move forward, or because he is still imprisoned by what happened, even now. An attempt to press Mafuyu for an answer results in him stating he does not know either and departing.
Waiting at the same spot Hiiragi is joined by someone else and he tells Shizusumi Yagi that he is so slow, and has just met with Mafuyu. Replying to his shocked reaction, Hiiragi denies he has been keeping in touch with Mafuyu only having met him at the station by chance the other day. Sharing that Mafuyu in a band now, Hiiragi feels it is so funny before having his hair ruffled by Shizusumi. He is told there is nothing for him to worry about, but he cannot help but worry for they are all childhood friends.
Texting Mafuyu to look outside his window Hiiragi is stood outside in the rain with an umbrella. Spotting Mafuyu he then calls him to come out and speak with him.
From 柊 (hiiragi), referring to the flowering plant known variously as 'holly osmanthus', 'holly olive', or 'false holly'. It seems to be combined from the stem of archaic verb 疼ぐ (hiiragu) meaning "to throb, ache," referring to the thorny and prickly resemblance of the leaves, and 木 (ki) meaning "tree."
- Hiiragi's zodiac symbol is a Taurus.