At first Kaguya was only interested in him as a swordsman who has an enigma, but later after seeing how much he cares about his comrades and her she starts to fall in love with him. She also affectionately calls him "Otōto" (
The 2 previously had a strained relationship due to them both being the presidents of opposing student councils in the school that absolutely couldn't stand one another. The hatred was only one sided as kaguya wanted to mend the relationship between summoners and swordsman. Their relationship became much better when the 2 councils were merged and kanea eventual joining of the harem.
However they were shown to be able to get along perfectly in a professional manner with Kanea volunteering to be on kaguya's side against kazuki during the election in order to make it difficult for kazuki.
Kaguya has a very friendly relationship with Hikaru as her close friend as well as vice-president.
Kaguya was the first person ever to call Koyuki by her name, she is very fond of her and doesn't seem to care that she is an elf.
Kaguya likes Miō as well as everyone in the Witch's House.