FamilyBoth of her parents are employed and not named. It is mentioned that she still has 2 other siblings younger than Taishi and Keika. It is mentioned that she has respect for her parents and takes great care of her siblings.
Episode 10 of Season 2 (Volume 9), Her little sister, Kawasaki Keika was introduced. It was shown that her sister was also participating in the Christmas collaboration event and Saki was dressing her up with a warm and generous smile of a mother. Saki calls her Kei-chan, Keika affectionately addresses her as Saa-chan. Keika is shown to be a happy, positive child who once spent her time playing with Hachiman, until Saki came to pick her up.
Saki was also taking pictures of her sister's performance in the Christmas event. In the light novel, their relationship was provided greater detail than in the anime.
She made an appearance again in Episode 12 where she learns to make homemade cookies along with her sister in the pre-Valentine's Day collaboration event.
In the anime version, her only conversation response is "unagi" (eel), when Saki asks her what she wants to eat.
Soubu High School
It was mentioned that Saki is friendless and a loner of Class 2-F. Saika says he hasn’t seen Saki being friendly with anyone.
Throughout the series she is shown to develop friendships and gain acquaintances.
Saki and Yumikio seems to be loggerheads and don't get along well. Most often they seem to be ready for a verbal spat. The fact that Saki rebukes others quickly is the reason for Yumiko to be hostile towards her and excluded Saki from her friend circle. Since Yumiko befriends people who are cute. Yumiko doesn't like Saki's cold and revolting outward personality, while Saki views Yumiko as a show off, who takes life lightly. They have a cold exchange at every encounter, making nearby people uncomfortable.But still they acknowledge each other. Saki listed Yumiko's name to Hachiman, as a suitable candidate for student council president. In Episode 12 of season 2 (Volume 11) Yumiko expressed her envy of Saki's cooking ability, as Yumiko didn't have any confidence in cooking. Both Yumiko and Saki agreed to have their request to be fulfilled together as one (pre-Valentine's Day event).
Saki is one of the few people to not to show any romantic interest in Hayama. She views him as a normal spoiled person. However Hayato once tried to have a conversation with her regarding her being tired in class due to her part-time job, But she ignored him making Hayato feel like he was rejected. He didn't mind and has no bad feelings, he was just happy to try and help
In Volume 11, Saki visited the club to request help with teaching Keika how to make simple Valentines chocolate.
They are classmates in class 2-F. Saki sits in the seat in front of Yui. Initially, Yui describes Saki as a little scary. They don't talk often and would not be considered friends. Yui thought answering the question "are you friends?" difficult to answer.
It was mentioned in Volume 11, that Yui addressed Saki by her first name, indicating that their relationship has deepened to an extent.
Yukino and Saki have a great number of similarities, as both act aggressive and unapproachable. Hachiman says, "If Yukinoshita Yukino was frigid, Kawasaki Saki was just cold".
In Volume 2 when confronting Saki at Angel Ladder, they display a similar enjoyment of insulting Hachiman. Hachiman soon interrupts their banter and tells them not to insult others (himself) in their spat.
Saki feels Yukino can't understand her, because she thinks Yukino is spoiled and/or rich. However, after the request, Saki wanted to thank Yukino through Hachiman, as she doesn't know how to approach Yukino, even though she now knows her as a good person.
In Episode 12 of season 2 (Volume 11), Saki summoned up courage to ask for help from the Service Club. She asked if Yukino could help her teach Keika to make simple Valentines chocolates. Yukino also described Saki's cooking of Rice Krispie Treats as cute in comparison to the similar sound of a cat in Japanese. This is the first time they are shown to have a normal conversation without any ill content like their former meeting.
Yukino is fond of cats, but Saki is allergic to them.
Also, both girls share an affection for the same boy Hachiman due to his helping them in a way.
Saki believes Hachiman takes life too lightly because of his jaded views on it. She also thinks he's an idiot after she read his career survey.
Later on, she acknowledges him and his reliability. She understands he is quite capable, as he's able to predict her motives for working and provides suitable remedies to her problem. She starts to respect Hachiman after seeing the sibling relationship between Hachiman and his sister.
Sometime after her request, her attitude softened towards Hachiman. She thanked him for helping her. Saki may be more open with him as she told him about her family affairs, despite her being a private person. Conversely, she still often glares at Hachiman when she is provoked, even threatening to punch him.
In the light novel, it is revealed that they are also classmates in summer cram school. Hachiman also acknowledged Saki. He is also able to predict her reasons for her aggressive nature. Hachiman influenced Yui to recruit Saki as a costume designer for the class play. After being included by others, Saki begins improving her social relationship in the class.
In episode 2 of season 2 (Volume 7) Saki was grouped with a portion of their class, including Hachiman, during the school field trip where she seemed to get along with everyone. She even held on to Hachiman's blazer when she was scared in the haunted house. This shows she trusts him to an extent.
In Episode 5 of season 2 (Volume 8), she acknowledged his leadership skills, this is shown when she included Hachiman's name on the student council president list, despite knowing he won't get enough votes to win.
In Episode 12 of season 2 (Volume 11), Saki seemed shocked and curious about Hachiman and Kaori, when Kaori asked Hachiman if she had given him any valentine chocolate in the past which hints at jealousy.
She may have developed feelings for him which can be noted from her behavior later in the series. She is either nervous or shy when crossing paths or talking to Hachiman. Saki would avert her eyes as soon as their eyes met, indicating shyness and sometimes she was shown to blush. Hachiman doesn't appear to pay her much mind so he may not be aware of her feelings for him or chooses to ignore them.
In the novel mostly, there is a running gag of Hachiman failing to recollect Saki's family name in his mind but this is seems to be a jab as he calls her last name clearly when addressing her. Hachiman more than once mentioned in his mind that Saki is good looking. Once Hachiman tried to ask Saki about Keika but forgot her name. While trying to recollect Keika's name, Hachiman accidentally came up with Saa-chan causing Saki to blush and fluster as that happens to be her nickname given to her by her siblings and family.
Saki seems to have respect for Komachi, as she quickly came to help the Hikigayas when Komachi called her through Taishi about the student council election issue. Also because Taishi gets along so well with Komachi.