Chiyo Aiba

is the younger sister of Izō Aiba.

Appearance
Chiyo is a young girl with dark hair worn in pigtails. She wears a light-colored sleeve over a black undershirt and vertically striped shorts. Chiyo always has a faint blush on her face.

Personality
Chiyo is a precocious girl, that is quite developed in terms of speech and intellect despite her apparent young age. She bluntly called Nene Ōmori a "barking woman" because of her brashness. In addition, she appears to favor things in the romantic sense as she follows the advice of her love fortune; upon sight, she has fallen in love with Beel.

She also holds a strong belief over fortunes as after reading one about a wonderful encounter on a southern island, she decides to accompany her brother to his class trip.

Okinawa Arc
Chiyo is first shown with her elder brother Izō when they arrive at an Okinawan hotel, sleeping in Izō's backpack. She remains asleep throughout most of the day. However, when Izō and Oga meet in the hotel's hallways, Chiyo awakens and sees Baby Beel, instantly falling in love with him.

The four head to Aoi Kunieda's and the Red Tail's room. There, she introduces herself and her brother asks why she likes Beel. She blushes and is revealed to like him because of his penis, but is embarrassed to say it and calls her brother a "perverted kappa" for being curious. She is again embarrasses when Izō claims she's on a play date with Beel. After that, she and the others are given sata andagi to eat and Aoi asks why Chiyo is accompanying her brother on the field trip. Chiyo explains that she likes reading and fortune-telling, interests that led her to a horoscope saying she'll have a wonderful experience on a southern island. She shows Aoi and Chiaki Tanimura a fortune-telling magazine and explains that she and Izō are Virgos. When Aoi reveals that she's a Taurus, Chiyo reads from the magazine and sees that Aoi has a strong love compatibility with Virgos.

The next day, she accompanies her brother on his "date" with Aoi, including Oga and Hilda. Chiyo later tells Izō how difficult it will be to make Aoi his woman due to her feelings for Oga. She is told that the situation is only making Izō more in love with her and is confused when he mentions having a reserve ally. She is then seen enjoying the marine animals at the aquarium, with Aoi holding her in her arms. She is just as confused as everyone else when Oga tells Aoi to "stop staggering about and just eat".

They enjoy watching the dolphin attraction at the aquarium and Chiyo decides to bring Beel closer to them. Along the way, they meet Futaba and a rivalry immediately sparks between her and Chiyo. Chiyo is asked about her age and birthday and reveals them to Futaba, then proclaiming herself to be Beel's future wife. The two girls begin to fight and eventually they ask Beel who he's more attached to, or loves, in Chiyo's case. When he retreats to Oga, they agree that he loves his father the most and decide to put off their feud until then. She is among the people who witness Hidetora Tōjō try to fight Izō. She runs to her brother after he's done fighting Tōjō.

Izō Aiba
She seems close to her elder brother and he often carries her in a backpack on his back. Aiba often describes Chiyo as being precocious and seems content with letting her doing things independently, implying a certain amount of trust between the two.

Beelzebub IV
Chiyo is very infatuated with Baby Beel and has developed this attraction after seeing his penis. However, Baby Beel is very intimidated by her. Chiyo once told Futaba that she is Baby Beel's future wife and blushed after saying the words.

Futaba Kanzaki
Upon their first meeting, Chiyo and Futaba have developed a rivalry about Baby Beel due to their affection for him. Chiyo does not think fondly of Futaba due to her calling Beel her "lackey". The two, however, have decided to put their feud over Beel on hold after seeing that he apparently loves Oga the most.

Quotes

 * (To Baby Beel) "Please call me Chiyo. Although I may be inexperienced, please treat me well."
 * (To Futaba upon their first meeting): "Just what are you to Beel?"
 * (To Futaba): "We'll meet again someday..."