kiga (famine devil)

With War Devil (Yoru):
This is the most explored and tense relationship. Kiga affectionately refers to Yoru as her "little sister" and says she would do anything for her. However, Yoru sees her as weak, crazy, and unsound, and doesn't reciprocate the affection (telling Asa to stay away from her). Kiga tries to use her in her plans (empowering her to face Death), which creates friction. Yoru underestimates her and is irritated by her personality.

With Control Devil (Makima/Nayuta):
Sisterly relationship, with a certain bond. Nayuta (the current Control) calls Fami/Kiga "sister" and they share a familial tie. Kiga seems to have a closer or more similar connection with Control than with the others. Both are manipulative, although in different styles (Control is more dominant, Kiga more anxious).

With Death Devil (the eldest, the fake Fami):
Kiga has a conflicted but mutually respectful relationship with Death. Both value humanity's existence in some way, but Kiga actively tries to thwart her older sister's plans (she wants Death to "disappear" to prevent further suffering). After the twist, Kiga ends up being manipulated/brainwashed by Death and forced to serve her, demonstrating her older sister's dominance. Kiga directly begs Death to disintegrate for everyone's sake.

Hair: Long, blonde, messy, and uneven. It falls in uneven layers, with stick-up strands, an irregular fringe that covers part of the forehead and sides, reaching the ears, and some longer strands that reach the collarbones. In fan art (like the first image you shared) it usually appears more silver/white, but in the canon manga it's blonde.
Eyes: Like the rest of the Four Horsemen, he has eyes with multiple concentric rings. In the manga they are usually green, although in some colored covers or fan art they appear in pink or spiral tones (as in your image).
Facial expression: Almost always nervous, anxious, or with tears in her eyes. She is the most visually "emotional" of the sisters: she cries easily, has a vulnerable and expressive face that contrasts with the poker face of the fake Fami.
Body type: Young woman with an adolescent/student appearance, similar to her sisters (Makima, Yoru, etc.).
Outfit:
Wear the standard Fourth East High School uniform (the school where much of the academic arc takes place). This includes:
White long-sleeved blouse.
Dark school skirt or dress (typically black or navy blue).
Jacket or elements of the school uniform.

Meek (submissive/timid), taciturn and extremely emotional: She is the most openly emotional of the Four Horsewomen. She cries easily, gets nervous, stammers, and shows vulnerability (for example, she cried throughout her school presentation and cried even harder when no one was paying attention). This contrasts sharply with Makima's coldness, Yoru's aggressiveness, or Death's composure.
Anxious and somewhat pathetic/cowardly: She openly displays fear and despair. She is nervous, feels inferior at times, and has a personality that makes her seem more "human" and weak compared to her sisters. She offers ridiculous amounts of money (like 2000 yen) to save her life in moments of panic.
Fatalistic with a twisted "benevolence": She believes human life is suffering and wants to "save" humanity by liberating it through death. She absorbs life (even from innocents or animals) without hesitation to heal herself, but does so with the idea that she is alleviating future pain. She is fatalistic but seems to have a twisted affection for humans (more so than other Horsemen).
Proud as a Devil: Despite her shyness, she possesses demonic pride. She refuses to perform "lower" tasks (like taking out the trash) because she considers it a waste of her superior talents.
Manipulative but less effective: She is calculating and has plans (she wants to stop Death to "save" the world), but her execution is more desperate and less masterful than her sisters'. She tries to use others (including Yoru) for her own purposes.