| 高山 ケイト|
|Age|| 15 (Vol 4~5)|
16 (Vol 6~onwards)
|Family||Maria Takayama (sister)|
|Novel Debut||Volume 4: Chapter 7|
|Anime Debut||Episode 8 (cameo)|
Due to unknown reasons, Kate takes up the role of a parent in their sibling relationship. She is overprotective of her little sister (calling Kodaka during the sleepover, every hour to check what Maria ate, to ask if she brushed her teeth etc.) and seems to take responsibility of her upbringing as well (making sure that Maria performs her duties and forcing her to eat healthy food). Kodaka speculates that she has a sister complex. She is also quickly angered by Maria's childish antics and often scolds her because of that. Kate is particularly jealous of Maria's friend-like relationship with Kobato, and also a bit envious of her loving attitude towards him.
Kate is grateful to him for taking care of her little sister. Because of this (and maybe some other prosaic reasons), Kate seems to like Kodaka. This explains her flirtatious behavior with him (for instance Kate teases Kodaka calling him onii-chan). She implied that she wouldn't mind being more than friends with him if he wasn't Sena's fiancee (to Kodaka's denseness).
Kate is especially thankful to Yozora, albeit doesn't know her personally. She thinks that Yozora was the first person to see a kid rather than a genius in Maria, and behave with her accordingly, though she also thinks that Yozora goes to extremes sometimes (like in the case with her telling Maria to bask in sunlight stark naked in order to not turn into a vampire).
She is a friend of the Chairman (they are fishing buddies). They both share their love for fishing and they like to spend time on this activity. During such times, Tenma seems to share his thoughts with Kate (as she already knew that Kodaka is Sena's fiance).