According to Eiki Shiki, Hecatia is eccentric but relatively not evil compared to most denizens of Hell. She seems capable of being caring and compassionate, especially towards her underlings (namely Clownpiece). When offered to, she denied the opportunity to rampage across the Earth, refusing to do so in front of innocent humans. Additionally, it might be possible that her personality changes when she switches between her three bodies.

Hecatia has an unwavering desire for personal freedom and dislikes authoritarians of any sort (somewhat matching her "unconventional" appearance). In particular, she has a strong distaste for the Lunarians, considering them to be the antithesis to her ideology. However, it's not known whether this specific dislike of them was due to her own personal motivations, or if she was convinced to hate them due to her close relationship with Junko.

Hecatia's ability allows her to exist on Earth, the Moon, and the Otherworlds all at once with different bodies, while her core soul resides in Hell. As places like Gensokyo and the Dream World are Otherworlds, Hecatia can access these as well. She can switch between them by wearing the respective astronomical objects on the top of her head. She can also summon them to essentially give herself clones.

Hecatia’s overall appearance is eccentric and comical; Sanae Kochiya even refers to her as a "weird T-shirt jerk" [Legacy of Lunatic Kingdom].

When designing her, ZUN intentionally aimed for a character who was "simple yet bizarre in appearance," giving her a comical expression that borders on the absurd. She can switch between different physical forms, each with a distinct appearance. When she manifests in a particular form, a corresponding celestial body—representing the world she is currently embodying—appears above her head; when she switches forms, this celestial body is replaced by another.

Her hair and eye colors also shift depending on the form she assumes: they are deep blue when she appears in her "Earth" form, golden yellow in her "Moon" form, and deep red in her "Otherworld" form. In Touhou Kanjuden , the transition between these forms involves a gradual shift in her hair and eye colors. While she most frequently appears in her "Otherworld" form, she visits Gensokyo in her "Earth" form in Touhou Sangetsusei V (Strange and Bright Nature Deity). In fan-created works, the "Otherworld" form is the most common, though depictions of her other forms also appear. She has long hair that falls past her shoulders, with bangs cut straight across her eyebrows. Around her neck, she wears a black choker connected by a golden chain to three miniature celestial bodies: Earth, the Moon, and the Otherworld. She wears an off-the-shoulder, black-based T-shirt emblazoned with the text "Welcome ❤ HELL"—the lettering is white, the heart is red—and the design is further accented with bright red floral motifs.

ZUN mentioned that, in his original concept, the T-shirt she wears would also change depending on her current form; one such idea—"I ❤ HELL"—was ultimately not implemented. She wears a pleated miniskirt with a black lining; the skirt is divided—from left to right—into three distinct sections colored green, red, and purple, all overlaid with a black checkered pattern. Barefoot.

Hecatia, like her would-be friend Junko, has a grudge with Chang'e. It was Chang'e's husband who shot down the suns, weakening the shadows of Hell as a consequence. However, it mostly seems to be through Junko's influence that her grudge exists. Because she sympathized with Junko, she decides to side with her in Legacy of Lunatic Kingdom.

Clownpiece is a subordinate of Hecatia, who allows Junko to use Clownpiece in her scheme against the Lunar Capital. Hecatia seems especially fond of her, letting her have a "vacation" in Gensokyo as a reward for finishing her "big job" in Legacy of Lunatic Kingdom.

Much light has been made of her fashion sense and unconventional modern outfit. Many fans have compared it to Scene, Goth, Punk, and Hot Topic fashion. As result of that, some even have referred to her as Hot Topic-chan or Hot Topic girl

Some Japanese fans dub her as "freaky T-shirt weirdo" (変なTシャツヤロー Hen'na tiishatsu yarou) or just "Strange T" (変T Hen T) from a conversation in Sanae's extra scenario.Because Sanae is the only player character who comments on Hecatia's shirt in Legacy of Lunatic Kingdom, Sanae is sometimes depicted wearing the shirt herself or continuing to make fun of Hecatia after the incident ends.Besides her own, sometimes she is shown to be a fan of odd t-shirts in general, such as this one from Danbooru.

A running gag in fandom has other characters putting unusual objects on her hat (or at least attempting to) with the intent to try and change her hair colors.

Hecatia appears as the main Extra Stage boss of Legacy of Lunatic Kingdom. It's explained that she joined forces with Junko to bring an end to the hegemony of the Lunarians in the Lunar Capital. Her trump card, if Clownpiece and Junko had failed in their invasion of the Lunar Capital, was to trap the Lunarians in the Dream World and hold them hostage, hoping that it would provoke an attack of some kind, which she could use to her advantage. She did not know that the Lunarians had threatened to wipe out all life on Earth, including Gensokyo, forcing the protagonist to begrudgingly fight for the Lunarians.

In the final battle, Hecatia and Junko joined forces to fight the protagonist together side-by-side.

During Marisa Kirisame's route, she mentions that she hates the leader of the moon rabbits, Chang'e, because "she is the wife of the guy who killed one of my stars". Said star, namely Apollo, seems to be one of the suns shot down by Hou Yi. If the sun is weakened, Hell would also be affected as shadows would become weaker as well.

Shortly after the events of Legacy of Lunatic Kingdom, Hecatia brought Clownpiece to Gensokyo and asked her to stay there and get used to the place. In Chapter 10, Hecatia appears in Gensokyo again to check on Clownpiece, and assigns her a new task asking her to encounter more lifeforce, especially from things that aren't often seen in Hell. In Chapter 13, she meets Reimu Hakurei and Marisa Kirisame, and talks with them about the stone cherries that are appearing in Gensokyo, affirming that those stones are nothing but the crystallization of the missing fairies' lifeforce, and saying that she wants to take them with her to Hell.

In Alternative Facts in Eastern Utopia, Aya Shameimaru interviewed Hecatia about the recent arrival of denizens of Hell, such as Clownpiece, in Gensokyo. In the interview, Aya expressed cynical views towards Hecatia and her cohort, wondering if they weren't planning some sort of invasion into Gensokyo to take it over and destroy its "charming atmosphere." Hecatia rebuked Aya and told her that maintaining an isolationist attitude would make Gensokyo no better than the Lunar Capital, and that Gensokyo had always relied on new youkai to ensure its culture didn't become stagnate and stale, echoing sentiments from an earlier interview with Yukari Yakumo. Hecatia also harshly chided Aya for frequently stretching and abusing the truth to gain attention and newspaper sales through manufactured outrage. Aya was apparently so disturbed by the interview that she decided not to publish it, and ended up cancelling that edition of her newspaper entirely.