|Full Name||Kuroba Fumiya|
|School||Fourth High School|
|Voiced By||Yumi Uchiyama (Audio Drama)|
|Novel||Volume 8, Chapter 4|
|Manga||Reminiscence Arc (Manga), Chapter 2|
|Audio Drama||Reminiscence Chapter|
Mitsugu is Fumiya's father.
Ayako is Fumiya's twin sister. She likes to tease her brother.
Tatsuya is one of their cousins who taught magic to him and his twin sister Ayako.
Fumiya has not looked down on Tatsuya, even when they were young. On the contrary, he greatly respects Tatsuya and aspires to be like him in terms of skill. He easily gets embarrassed whenever he is praised by Tatsuya, which is usually followed up by teasing from Ayako, which usually results in him getting flustered. Fumiya and Ayako are one of the Tatsuya's information sources.
Although Fumiya loves and respects Miyuki like an older sister just like Ayako, he reveres and admires Tatsuya even more than either of them.
Miyuki is his second cousin. He refers to her as "Miyuki- nee sama". He loves and respects Miyuki as much as he does Ayako; like an older sister.
In Volume 16, Fumiya was the first to give up his claim to succession as the Yotsuba head in favor of supporting Miyuki as the next head of the family.