; :The lead character of the story, he's stunned to learn that not only will he change into a girl when he becomes excited, but somehow he failed to notice that all of the other members of his family switch sex as well. His new female form is just as strong as his male form, and has a power of attraction that quickly launches her into a career as a
Japanese idol. His family name is a reference to the word
futanari. ; :Futaba's love interest, the fact that he turns into a girl when he becomes aroused places a seemingly insurmountable barrier to their relationship. Her cooking is intolerably sweet to anyone else, and she is very
superstitious. After she switches from swimming club to
wrestling club so her new friend "Futaba
-chan" will not be the only girl in it, there is a joke about how it turns out that none of the other swimmers actually know how to swim in regular water that is not filled with dissolved sugar from Misaki's sugar-filled body. Her family has a little connection to the Shimeru clan. ; :Futaba's sister who in her male form makes the most out of her powers of attraction, by seducing countless girls and probably a few boys as well. She does not use
birth control, and leaves a small army of sex-shifting offspring behind. She also gropes Futaba, but probably more for the amusement value of watching his reactions than genuine interest since it does not cause her to shift sex. Futana genuinely loves both sexes, even to the point of shape shifting in front of Futaba whom he tricked to do sexy poses. ; :A very important member of the main Shimeru family which has arranged for her engagement to Futaba. Imperious and pushy she is initially contemptuous of her fiance until she learns that he's also the famous Futaba-chan and that he's already interested in someone else, at which point she desperately tries to win his affection. In her female form, she is short and unattractive, but her male form is tall, handsome and surrounded by a cloud of
pheromones that leave women awestruck. She uses this power to get free food since the transformation makes her extremely hungry. ; :The president of the wrestling club, Motomura is a large and impressive manly figure but is easily moved to tears in his excesses of emotion. He is also a compulsive
gambler and Negiri takes great advantage of his weakness. ; :Another member of the wrestling club, he's the weakest wrestler among them, and a would-be
lothario. ; :The last member of the wrestling club, he takes the Japanese
cliché of
nosebleeds due to sexual arousal to exaggerated lengths, even using it as a weapon in a martial arts tournament. ; :A famous actress/model, s/he is the person Futaba thought of as his father, although he actually gave birth to Futaba. Iroka pushes Futaba to follow in her footsteps as Futaba-chan. ; :Misaki Shima's friend, she takes control of both the wrestling club and Futaba-chan's idol career because Motomura and Futaba are both easily taken advantage of. Negiri is Futaba-kun's equivalent of
Nabiki Tendo and speaks using
Kansai turns of phrase. ; :A small man with an over-sized head, Principal Hiroin is somewhat mad. Whenever he sees someone in trouble he changes into one of his superhero costumes (modelled on Japanese superheroes) and appears to attempt to save the day. He is aware of Futaba's double identity and arranged for both identities to be students at the school, which has many secret cubbyholes where Futaba (and Principal Hiroin) can change identities without being seen. His daughter, Takane, is secretly Queen X and playacts at supervillainy just as he plays at superheroics. ==References==