Hiiragi Kashima's relationships and interactions with other people in the Given series.
Hiiragi seems to recognize Mafuyu after encountering him with Ritsuka and raises the matter of the guitar on his back and whether it is Yuki's. Hiiragi states that he thinks of Mafuyu as a younger brother and that they always used to get into small fights when they were younger.
Hiiragi knows the whole story of Yuki's suicide and was also aware of his relationship with Mafuyu
Ever since Yuki and Mafuyu hung out together during childhood, so did Hiiragi and Yagi.