Chiaki Tanimura is a supporting character in the Beelzebub series, known for her role as a core member of the all-female delinquent group called the Red Tail, serving under the group's leader, Aoi Kunieda. Her name is also spelled Chiaki Tanimura.

In terms of appearance, Chiaki is a slim and petite young woman with a short, evened fringe of black hair. Her most defining physical trait is her consistently deadpan expression, which rarely changes regardless of the situation. She wears the standard Ishiyama High School uniform, but a key element of her attire is hidden beneath her skirt, where she straps her modified airsoft guns to her thighs.

Chiaki's personality is largely defined by her quiet and reserved nature. She speaks very little, often preferring to communicate through hand gestures, nods, or simple expressions. Despite her default stoic demeanor and her readiness to use her guns without hesitation, she possesses a more traditionally feminine side. She is often noted to find girls who make cute or innocent faces adorable, a sentiment she frequently expresses towards her leader, Aoi. Her personality undergoes a notable shift when it comes to video games; in this context, she becomes much more talkative and competitive, even practicing all night to prepare for a match or to avenge a previous loss. She also has a younger brother, who often asks her to play two-player games with him.

Chiaki's primary motivation is her deep loyalty to Aoi Kunieda and the Red Tail. She respects Aoi as a strong and protective leader and is one of the first to recognize Aoi's romantic feelings for Tatsumi Oga. Her role in the story is that of a steadfast supporter. She often appears alongside her close friend and fellow Red Tail member, Nene Omori, confronting Oga or participating in the various conflicts that arise at Ishiyama High and beyond. During the Saint Ishiyama Academy arc, she takes on a cheerleader role to support her peers. She is also a reliable fighter, using her marksmanship skills in battles against rival groups like the MK-5 and the members of the Shadow Force.

Chiaki's relationships are central to her character. Her bond with Nene Omori is particularly strong, as they are frequently seen together and are considered close friends. Her respect and affection for Aoi Kunieda are absolute, and she is deeply protective of her. Conversely, she has a strong dislike for men who flirt with or harass Aoi, and she is known to shoot such individuals on sight. Her attitude softens slightly towards Oga, as she realizes that Aoi is in love with him. Her interactions with other characters, such as Furuichi, are often marked by her referring to him as trash or gross, showing a general disdain for his behavior.

In terms of development, Chiaki remains a fairly static but dependable character. Her most significant moments involve her emotional barriers breaking down. For instance, when Aoi triumphantly reclaims her title as leader of the Red Tail, Chiaki is moved to tears of happiness, a rare display of emotion that highlights her deep investment in her leader's well-being. She also expresses genuine shock and horror when witnessing a Poltergeist's face melt away, showing that beneath her cool exterior, she is not immune to fear.

Chiaki's notable abilities lie in her expertise with firearms. Although she shows minimal physical strength in hand-to-hand combat, she is an expert marksman with her dual modified airsoft guns. She keeps at least four guns on her person. Her signature technique is called Simultaneous Barrage. To execute this, she fires her two currently wielded guns, tosses them into the air, quickly draws her other two guns, and continues firing before repeating the cycle. This allows her to maintain a constant and rapid stream of shots, making her a formidable ranged fighter.