Natsumi Kuzuryu

Fuyuhiko Kuzuryu's Sister is a minor character in Danganronpa 2: Goodbye Despair.

She was the late younger sister of Fuyuhiko Kuzuryu. She was killed by a fellow student named Sato, who covered it up along with Mahiru Koizumi, blaming it on a fake serial pervert. Her death was avenged by Fuyuhiko, who in return killed Sato.

This accident was revealed in the Danganronpa 2: Goodbye Despair's second motive, Twilight Syndrome Murder Case. In one of Fuyuhiko's free time events, it's revealed that his sister's title was Ultimate Little Sister (超高校級の「妹」chō kōkō kyū no “imōto”).

Appearance
In Twilight Syndrome Murder Case, Fuyuhiko's sister has long blonde hair and wears the Hope's Peak Academy uniform. She also seems to be fairly taller than her brother.

Personality
In Twilight Syndrome Murder Case and according to Girl E, Fuyuhiko's sister was described as a mean and egotistical girl who would plant hatred towards someone she dislikes or envy. Fuyuhiko's sister is also said by her parents to be much more violent than her brother and more worthy of being the Yakuza heiress.

As described by Fuyuhiko, she was used to making a fool out of him everyday and always pissed him off, but Fuyuhiko always considered her as his cute sister. When she cooked fried noodles during the temple festival, a huge line would form outside the temple. She also got an insane number of contracts from hand towel companies. She is self-centered, selfish, and extremely arrogant. However, she had a subtle way of making people do what she wanted.

1st Day
Fuyuhiko's sister's corpse was found by Mikan Tsumiki, Hiyoko Saionji, Ibuki Mioda, and Mahiru inside the music room, after her killer, Sato escaped and locked the door. Sato lied to them, saying that she heard something inside the room, where she murdered Fuyuhiko's sister.

After Sato suggested the group to borrow the key in the staff room, Mahiru seaks into the staff room and she grabs the key for the group. However, something unexpected happens when they enter the room. They find Fuyuhiko's sister, lying dead on the floor.

The group quickly panicks, but Hiyoko suggests them to remain calm, as she finds out that the girl who was lying on the floor has recently been killed, and that the killer may still be around. Hiyoko decides that the culprit probably locked the music room's door from the inside out and then, after murdering the girl, they broke the window and escaped through it. The group decided that the culprit panicked after clubbing the girl, so they accidentally broke the aquarium and made the gravel scatter all around. It was proven when Ibuki took the key, which had been in the staff room as usual, and showed that the only two ways to lock the music room are from the inside or with the key from the staff room. So the group reach the same conclusion: the culprit escaped through the window. Sato convinces the group that a pervert committed the murder, because her swimsuit had been stolen recently. In the end, the group decides not to get involved in the case and leaves the corpse one by one, the last being Mahiru, who still seemed confused about what happened that day.

3rd Day
The truth was revealed on the 3rd day. Sato was first shown approaching Mahiru who had been waiting for her arrival in the Academy's backyard. Mahiru wanted to show Sato a picture that she took just yesterday. It's a picture of a broken flower vase in the classroom next to the music room. Mahiru thought that the glass breaking noise yesterday was not the sound of window breaking, the culprit didn't escape through the window and, finally, Mahiru knew that Sato was actually the culprit. Mahiru decided to clean up the evidence by erasing the picture she took yesterday.

Finally, Sato admits her crime and tells Mahiru that Fuyuhiko's sister, the girl that she murdered yesterday had been giving Mahiru trouble. Sato knows the girl was Mahiru's junior at the photography club in junior high. She couldn't stand it anymore that the girl was using her parents' status to bully others. At first she tried to just talk to the girl, but then the girl said she was going to go after Sato too, so she got angry, and before she knew it, she was strangling the girl and she lost consciousness, so before the situation got even worse, Sato killed her. Sato becomes flustered and leaves Mahiru alone.

Fuyuhiko Kuzuryu
Fuyuhiko is her older brother. She and Fuyuhiko both care about each other, as evident by Fuyuhiko taking revenge on her by killing her murderer in the same fashion and when Fuyuhiko's sister was given the chance to take her brother's place as Yakuza Gang Leader, she declined knowing it would hurt her brother's feelings. She got her talent “Ultimate Little Sister” because of her brother's influence as a Yakuza.

Mahiru (Girl D)
Fuyuhiko's sister holds a grudge against Mahiru and bullied her frequently. Mahiru and Fuyuhiko's sister had photography together and the girl was apparently jealous of Mahiru, (Due to her photos being better than Fuyuhiko's sisters) and then Fuyuhiko's sister than started picking on Mahiru.

Sato (Girl E)
Fuyuhiko's sister and Sato haven't met formally. After Mahiru told Sato that Fuyuhiko's sister as bullying her, Sato was quick to confront her about it. Despite Sato's attempts to sort things out peacefully, the girl replied saying that she would start bullying her as well, causing Sato to strangle her, and eventually decide to end her life.

Quotes

 * “I don't want to lead the clan. The reason I'm so amazing is because I'm your sister...” (to Fuyuhiko Kuzuryu)

Trivia

 * Members of Japanese mafia organizations or "Yakuza" tend to refer to each other using terms describing members of the family - the head of the organization and their spouse being "Father" and "Mother". All other members refer to each other as "Big Sister", "Little Brother", etc. based on age, ranking and seniority. Thus, the title of "Little Sister" Fuyuhiko's sister was given actually refers to her status as a young member of a Yakuza family.
 * In Danganronpa: Trigger Happy Havoc IF, she is mentioned by Makoto Naegi when he gains his memories and he says Yasuhiro Hagakure was trying to sell his organs to "that Kuzuryu girl", most likely refering to her.