- "A brat who can't live without his parents' protection... is no match of me."
—Kuina in the manga Chapter 25
Hikari Kuina is a character first appears in the Beach arc and later revealed to be a trans woman. Originally specialized in clubs (balanced games), after facing her troubled past with her stern father, she redefines herself as a spades (physical games) player.
Detailed in the manga Chapter 25, Kuina was born to a dōjō master and expected to become his competent successor. In order to relieve the tension between her harsh father and considerate mother, Kuina did her best to perfect martial art but was always scolded by her father for not delivering the decisive blow on her opponent. Kuina is revealed to be a trans girl. Her mother was likely aware of her sexual orientation and, unlike her father, encouraged Kuina to follow her own path. Eventually Kuina left her home and received sex reassignment surgery. She worked as a boutique clerk which she states that she always got herself in troubles. Some time later, Kuina rushed to her mother's hospital upon learning the divorce of her parents and her mother's weakening health, Kuina vowed to take care of her in the remaining life. Around that time, Kuina has been sent to the Borderland and determined to return to the original world to reunite with her mother.
Kuina teams up with Chishiya to plan to steal all the cards from the Beach society, because they are told only one person with the complete suit of cards would be allowed to leave the Borderland. When Ryōhei Arisu and Yuzuha Usagi have arrived at the Beach, Kuina approaches them to decide if they are suitable to be their accomplices. Kuina first tries to befriend Arisu by telling her reason for returning to the original world and warning him not to get in trouble with Aguni's "martial sect". When Arisu finds out the disposed human corpses outside of the Beach, Kuina and Chishiya reveal their plan to him.
Unbeknownst to Kuina, Chishiya only informs Arisu to access the baiting safe which leads to Arisu and Usagi's apprehension. Just before Chishiya is about to leave the Beach with all the cards, Kuina stops him in time to drag him into the Witch-Hunt game. Realizing Chishiya's true color, Kuina wanders around and learns from An about her intent to analyze the fingerprints in the crime scene. To let An proceed her analysis, Kuina defends her against Last Boss, who is under Aguni's order to kill everyone in the Beach with his katana. Albeit initially hesitated, Kuina recollects her time when she was a boy and being trained by her father of martial art. She successfully disables Last Boss from carrying out massacre, but is no match of Aguni and is rendered unconscious.
After surviving Witch-Hunt and King of Spades' attack, Kuina joins Arisu, Usagi, Tatta and Niragi to challenge the King of Clubs and wins at the cost of Tatta's life. Knowing Arisu's decision to stop playing any more game, Kuina clears the Jack of Spades alone and reunites with Arisu and Usagi again before the entrance of Queen of Hearts' arena.
- Kuina's alias coincides with Quina Quen from Final Fantasy IX, a party member with unstoppable appetite and ambiguous gender.