Hiyoko Saionji || F4A

Hiyoko is a short girl who appears extremely young. At first sight, Hajime remarks that her voice and her appearance don't give off the air of a high schooler at all. She has long blonde hair that is generally seen tied into thick, curved twin tails with two yellow-green ribbons, a white cat face accessory pinned in the center. Her bangs are curled and swept to the right, with two locks of chin-length hair curling outwards and framing her face. She has large, round, pale orange eyes.

Her clothes consist of a traditional orange furisode kimono with a floral print pattern that consists of white and yellow blossoms, and a yellow-green obi sash printed with tiny, darker yellow-green cat head silhouettes tied around her waist and secured with a bow at the back. Her footwear consists of zori with orange straps.

Hiyoko's cute appearance, voice, and (initially) her way of talking give off the impression she is innocent and childlike. However, in her introduction alone, it is revealed that she is very direct and cruel with a side of malice. She squishes ants while telling Hajime Hinata that they make a satisfying popping noise if done correctly, and even invites him to join her. Later at the beach, she goes around trying to step on and trample the crabs, laughing as if it were just child's play, showing an alarming fascination with it. She also stomps on and tear out flowers for her own amusement, explaining that she likes to destroy pretty things.

While not violent towards people (presumably due to her diminutive stature), Hiyoko often shows similar mean behavior towards them. When Hajime refuses to squish ants with her, she calls him a wuss. She constantly judges others and patronizes them with rude insults, and sometimes with swearing. She focuses on victims who get the most upset by her behavior and can be expected to not fight back, Mikan Tsumiki and Kazuichi Soda being the most common. She often takes a jab at Akane Owari as well, though she, unlike Mikan or Kazuichi, doesn't cry or get frustrated but actually takes her pranks into consideration due to being very gullible. One time, when Hiyoko was stomping flowers, she answered Akane's questioning by claiming that "stomping and kicking your food before eating it gives you a lot of more protein". Then, Akane actually started eating the stomped flowers. Due to Akane's gullibility, Hiyoko notes that she isn't that fun to bully. Out of everyone, she appears to dislike Mikan the most, and she has mentioned that she suspects Mikan is only acting to get attention. However, in her last Free Time Event she reveals that Sonia Nevermind is in fact the one she dislikes the most, due to how much attention she gets from the other students.

Hiyoko feels a sense of superiority, claiming that other people exist to serve her and she doesn't need friends. Because of this, Hiyoko tends to manipulate others to do her bidding, like telling Akane to investigate the motel on the third island under her request. During her Free Time Events, she also orders Hajime around and wants him to be her slave. If she doesn't get what she wants or if other people actually talk back to her, she tends to cry crocodile tears loudly like a child. Though her tears are sometimes genuine, her dishonesty makes it difficult to discern when she is experiencing sincere distress and when she is being emotionally manipulative, in a "boy who cried wolf" effect. It seems that she is somewhat spoiled due to being an heiress of her Clan, and as a result, she cannot do some things by herself, like tying her own kimono. In Danganronpa 3 Hope Arc, when her class fights against the Super High School Level Elite Task Force, Hiyoko appears to be the only one panicking and unable to defend herself, instead, shouting for help.

Due to coming from a traditionalist family, Hiyoko loves Japanese traditions and culture very much and tends to act condescending or even openly insulting towards other cultures. She considers many Japanese things "delicate, refined and high quality". She is especially fond of Japanese cuisine and candies, claiming that foreign ones are too sugary and gross and the people eating them are gross as well. She has described some other countries as worthless and compared their people to stupid animals, thinking that Japan doesn't need to import from them. As a rarer good trait, however, Hiyoko is stated to be willing to protect old traditions in danger of disappearing and she thinks people should take good care of the things close to them. She has also stated that she knows her thinking is old-fashioned, but she doesn't intend to disagree with new directions, just to protect old ones that need to be protected. Despite her traditionalist upbringing she has a lot of more unconventional interests such as heavy metal (being the only person in the class who liked Ibuki's performance) and horror movies.

Hiyoko acts very different towards Mahiru Koizumi after becoming attached to her when she helped her take a shower and showed her how to tie her obi. Afterwards, she refers to Mahiru as "big sis" and acts very affectionate towards her, often happily wanting to hold her hand or hug her and even give her a kiss. Though reluctant and a bit embarrassed at first, Mahiru went along with it and became close to Hiyoko, and the two are seen almost always together. Hiyoko has stated that she likes Mahiru because she is normal and not weird like the other students. In Island Mode and her Free Time Events, she also grows fond and protective of Hajime as a big brother figure, because he reminds her of her father who is very dear to her.

Hiyoko has been through a lot in her childhood due to her status as an heiress, explaining some of her mean personality. With her overbearing grandmother, and jealous people playing lots of cruel and even potentially life-threatening tricks and threats on her, she became very distrustful of other people and seemingly developed her mean personality to defend herself. The only person she trusted and felt safe with was her father, who was different due to being related to the family only through marriage. Due to her past, Hiyoko absolutely hated being deceived, as shown in Chapter 2 when she felt annoyed and flustered by Monokuma's invitation that was actually made by Nagito Komaeda. In Chapter 3, she directly told Hajime that she hated being deceived by others.

In spite of her negative features Hiyoko was quite a level headed person being the first in the game to accept the reality of Byakuya's murders and telling the class they need to investigate his murder or they'll all die. She strongly hates murder, condemning Teruteru after his death, begging the class to just hurry up and vote for Peko after Peko continues to personally insult Mahiru while in her sparking justice persona and being the only person in class 77 who calls out Fuyuhiko Kuzuryu for his direct role in Mahiru's murder.