Yoshikawa Yuki (吉川 由紀 Yoshikawa Yuki) is a close friend of Kyouko's, she attends the same high school.
Yuki has short blonde/light brown hair that goes to her shoulders and big beautiful yellow eyes. She is seen wearing her jumper most of the time and rarely shows her hands.
Yuki is a typical bubble head and very ditsy. Like Hori, she creates a fun and happy atmosphere. She is quite lazy and tends to sleep in class. Yuki is easy to get along with and makes friends quickly such as Miyamura. Yuki often tries to hide her negative feelings especially in front of friends, pretending that she's alright and actually doesn't care. It is remarked by Hori Kyouko that when Yuki doesn't want someone to know something, the more she tries to smile and hide it. The more she doesn't want to let go of something, the less she talks about it. As she is really reserved when it comes to her own feelings, she never tells anyone how she really feels or what she really wants. Due to this, the things she loves often are out of her reach.
Not widely known by the characters in Horimiya, Yuki is quite a jealous character. When Kouno Sakura is seen with Ishikawa Tooru, Yuki shows hesitation in her actions and has once accidentally acted cold towards Sakura. Yuki tries her best to hide any jealous feelings she has towards Sakura and be a good person. Instead of letting her jealousy come over her, she tries to do the right thing though because she has negative feelings towards Sakura, she feels pathetic for thinking of doing bad things.
It is also possible that Yuki may have a inferiority complex as she makes negative remarks of herself such as her being pathetic and states that Tooru is even nice to someone like her (hinting that she thinks lowly of herself?).
At the beginning of the series, Yuki had a crush on Miyamura, believing that he was Hori's cousin called "Konoha". A while later she finds out that Konoha is Miyamura and decides to give up on him. Though it is not canonically been confirmed by Yuki herself, it is heavily suggested that Yuki holds romantic feelings for Tooru.
Yuki is seen in chapter 1 asking her friend to copy her homework.
Hori is Yuki's classmate and best friend. Yuki usually asks Hori to hang out, but Hori declines. Yuki is supportive of Hori and Miyamura's relationship. Yuki even confides with Hori, such as when Yuki talks about Hori's "cousin," Konoha, who she likes (which is Miyamura). She is also quite reliant on Hori, especially with school work. Although they're best friends, Yuki still doesn't know much about Hori outside of school, since Hori tries to hide this from everyone.
She is often encouraged by Hori, such as learning how to bake, and is someone she can usually rely on for help. An example would be when Yuki wanted to reject someone's feelings and didn't want to hurt them
Yuki has little interaction with Miyamura, but they seem to be on good terms. At first Yuki thought Miyamura might have been a hardcore otaku who collected figurines, although that has changed. Unbeknown to her, Miyamura is the boy she likes, since she doesn't recognize Miyamura when his hair was up, and believes that he is Hori's cousin. After being told about who her crush really was, she gave up on him.
Because of Hori, Yuki, along with Ishikawa, have been seen to flock around Miyamura during classes to work together for projects.
Yuki and Toru are good friends, and they usually tease or make fun of one another. They both enjoy watching the uproar Hori and Miyamura cause. They also seem to hang out a lot since Miyamura and Hori started dating. Sometimes, there are small hints that both Yuki and Toru have some kind of romantic feeling for each other, but none of them realize it. But now, it is clear that Yuki definitely likes Toru even though she tries to deny it. Now, she is pretending to be dating with Toru to reject Yanagi's confession.
Although it is not directly put across, she seems to be in a relationship with Toru as shown in Chapter 65.