Joutou Kotobuki (寿 常套, Kotobuki Joutou) is a member of the Kotobuki family, and was one of the six suitors who took part in the second Jet Black Wedding Feast to marry Medaka Kurokami.
Kotobuki seems to have no qualms showing off her body; aside from her casual clothing, her sleepwear exposes her panties, and at the South Pole, she is the only suitor who does not wear gloves, despite the low temperatures. Kotobuki is a highly pragmatic fighter, using her style when needed and falling back on standard battle methods as necessary. She also has no qualms about using infants as hostages to hinder her opponents, stating that for the sake of winning, any measure is acceptable. Kotobuki speaks with a slight lisp.
Kotobuki has long, pink, wavy hair that reaches down to her lower back and light brown eyes. She wears provocative clothing that exposes her cleavage and abdomen, and a very short skirt, accompanied by fishnet stockings and leather boots. At the ruins of Hakoniwa General Hospital, Kotobuki wears a very revealing nurse outfit with a nurse's cap. When participating in the 100 Flowers Run, Kotobuki switches back to her original outfit. She has a tattoo on her tongue.
Jet Black Bride Arc
Kotobuki appears on the aircraft carrier Black after Najimi Ajimu manages to defeat the six doubles the suitors had sent in their place. Later, at the Black Bunker in the South Pole, Kotobuki is seen drinking with the other suitors. On Kuromaku Island, Kotobuki, Medaka, Bukiko Udou, and the remaining suitors prepare to leave for the moon. She makes no comment as Udou loses her temper with Medaka.  She is surprised when a jet crashes into the rocket. Kotobuki is unmoved when Bukiko Udou runs Zenkichi Hitoyoshi through with her spear. Udou tells the remaining suitors to wait until the rocket can be prepared. Kotobuki listens to Momo Momozono's offer for a release of the hostages, with conditions, making no comment as the other suitor dictates the course of the Jet Black Wedding Feast. Prompted by Medaka, Kotobuki sheds her spacesuit and names herself.
The group makes their way to another area to start the final round. Kotobuki and the other two suitors stand together in the new area, opposite Medaka, as the rules of the game are laid out. Kotobuki stands beside Kakegae Yuzuriha and behind Momozono as the game begins. Drawing a three of clubs from Udou, it is determined that Kotobuki will go third. The four each take a seat at a table as the game starts. She is surprised when Medaka chooses to leave the room. Angered by Medaka's behavior, Momozono makes an offer of alliance to the other two suitors. The game goes forward without a hitch, each player putting forward a word at each hour. Kotobuki listens to Momozono's explanation without comment. She is surprised when Momozono continues with the game in mid-explanation, and is shocked to realize she has been disqualified, rising from her seat in agitation. Kotobuki listens on as Momozono reveals Medaka's true plan; to force the suitor to end with "surrender" by manipulating the entire audience not to use the necessary syllables.
Unknown Shiranui Arc
After the conclusion of the Jet Black Wedding Feast, Kotobuki is reportedly doing well. When Hansode Shiranui arrives at the ruins of Hakoniwa General Hospital, Kotobuki is waiting for her with Fukurou Tsurubami and Yuzuriha in the director's office. Both women are wearing nurse outfits. After Fukurou kills Shinkirou Kotobuki and seals him in a name card, he hands the card to Kotobuki. Kotobuki tucks it between her breasts. She is revealed to be one of the only two suitors to have known the full extent of Fukurou's plans, the other being Kotobuki. When Medaka's group arrives at the hospital ruins, Kotobuki is the first to notice, and warns Fukurou. Fukurou orders Kotobuki to greet Medaka, promising a grand welcome. At Shiranui's request to keep Medaka away however, Fukurou instead orders Kotobuki to chase Medaka off. Kotobuki makes her way to the bottom of a staircase, where she begins using her style by singing the Edo Lullaby. Kotobuki leaves the staircase however, instead leaving a cellphone to project her song, as she sneaks up on Medaka's group. Having successfully reduced four of the members to babies, Kotobuki scoops up Zenkichi Hitoyoshi, remarking that babies are cute because they are easy to kill. She is surprised when Zenkichi hits her, and tells him to settle down. Noticing that Medaka has escaped, Kotobuki remains unruffled, confident that the younger woman will not stray far from her friends.
Kotobuki playfully asks the babies where Medaka is. Of course, the babies do not have a coherent answer. Seeing that Zenkichi looked away from the vent when she asked, Kotobuki pulls out a submachine gun and blows out the vent. Expecting Medaka's dead body to pop out, Kotobuki is surprised to see the vent appears empty. Kotobuki starts singing again. Not seeing any trace of Medaka, Kotobuki gives up the search. She smiles, thinking that Medaka went ahead alone, which would give Yuzuriha, an easier job. In the middle of Kotobuki's monologue, Medaka punches through the floor and jumps out behind her. As Medaka is about to attack Kotobuki, she finds the babies are strapped to Kotobuki like a suit of armor. Medaka pulls back, cursing Kotobuki. Kotobuki challenges Medaka to attack her and harm her friends. Kotobuki accepts her victory, and thinks back on how the other suitors relied too heavily on their styles, or not enough. When Medaka begins singing however, Kotobuki loses her cool, and attempts to shoot Medaka. With her eyes closed, Medaka gracefully dodges the bullets and slides closer to Kotobuki. When Medaka finally reaches contact distance, she kicks Kotobuki, sending a vibration that only harms her target and not the babies. As Kotobuki drops, Medaka tells her to sleep. After being defeated, Kotobuki is tied up by Namanie Nienami, her style having worn off.
An unconscious Kotobuki is carried to Fukurou's office by Yuzuriha, where Medaka is preparing her final attack on Iihiko Shishime. Kotobuki watches on as Medaka launches herself at Iihiko. She is surprised like everyone else by Medaka's clone gambit. When Iihiko dodges, she is appalled. Kotobuki and the others are protected by Medaka as Iihiko destroys the hospital. Kotobuki and the others are attacked by Iihiko; however, Kotobuki is saved by Yuzuriha. The two discuss Medaka's behavior, neither of them able to understand why she is going to such lengths for a single friend. Kotobuki uses her style to bring Zenkichi back to life. She explains that Zenkichi was the only one she could revive. She reminds Zenkichi that her style is not permanent, and when it wears off, he will be back to being dead. Kotobuki discusses Zenkichi's chances of winning with Nienami and Yuzuriha. She is surprised to see Iihiko dodge Zenkichi's kicks, and is further shocked when Zenkichi intentionally takes one of Iihiko's attacks. She is stunned as the situation reverses itself. Kotobuki watches as Iihiko is defeated. With his defeat, Iihiko's damage becomes reversible, and Kotobuki is healed by Medaka with the Five Forks. She is unimpressed by Nienami's behavior. After Kumagawa knocks out Medaka's friends, Kotobuki and Yuzuriha catch Kamome Tsurubami.
Bouquet Toss To The Future Arc
Nursery Rhyme User (童謡使い, Douyou Tsukai): Kotobuki's style allows her to manipulate nursery rhymes. As Kotobuki sings, those within a certain range start to revert to a younger form. As they get closer to Kotobuki, the target progressively gets younger and younger. This does not only affect their size, but reverts them to their style of dress and items that were on their person at the time. If the target is wounded, the de-aging will remove their wounds as well, as they did not have them at the time. The victim's age does not decrease in a linear fashion; instead, the target's age is reversed geometrically. Kotobuki's lullaby works on an infrasonic sound level, and can therefore affect her targets even if they cannot hear anything. As Kotobuki increases the volume of her song, the range at which the listeners will be unaffected shrinks. However, there does seem to be a limit on the style's effects; once reduced to infants, the victims will not grow any younger. With her style, Kotobuki can even bring the dead back to life. Kotobuki's lullaby can even be transferred through devices such as a cell phone, ignoring the laws of physics. Because it is centered around song however, Kotobuki cannot utilize her style if she cannot sing, for such reasons as her throat being too dry. Kotobuki's version changes the lyrics of the original Edo Lullaby; Kotobuki calls her song the "Little Kid Loli-by" (子ロリ歌, Kororiuta). If Kotobuki is knocked out, the effects of her lullaby will wear off.
- Red Carpet (幼稚赤掛け, Reddo Kāpetto): Kotobuki ties her victims (once they have been reduced to babies) to her body in order to form armor. While the babies themselves do not provide much physical protection, they do make the opponent reluctant to attack for fear of harming the children.
- The mark on Kotobuki's tongue is 幼, which can mean "Childhood" or "Infancy". Of the stylists shown thus far, Kotobuki is the only one whose tongue marking is not written in the kanji of her style.
- Because her style allows her to make people younger, Kotobuki matches Shinkirou's fetish for a young girl.
- (To Zenkichi Hitoyoshi) "Babies are sho cute. Sho little, sho soft, sho warm and full of life. They're sho eashy to kill. They're jusht sho damn cute."