Yumiko is a timid, quiet nun with dissociative identity disorder and is a pacifist who is easily frightened and acts in a somewhat cute but timid manner. However, when she takes her glasses off, her other identity, Yumie, is unleashed. Yumie is impulsive and violent, showing no fear of anything and preferring to negotiate using the sharp end of her katana. She seems to genuinely enjoy killing people, having almost superhuman strength: she is adept enough to kill her victim from outside the room, and is capable of smashing heads into walls with her bare hands. Yumiko has often commented how hard it is for her to "get Yumie to sleep" after she has been provoked into action. Her raw strength, fearlessness and fearsome katana skills make her the ideal partner to Heinkel, who is cool-headed and analytical. Both Yumiko and Yumie are devout to their religion; however, Yumie is loyal to her church to the point of fanaticism, and is glad to slice down anyone she sees as a "heathen".
Yumiko always dresses in a standard Catholic nun's uniform, which consists of black robes, a nun's hooded cowl, a white scarf, and white gloves and white stockings held with a garter belt and black boots. She has long black hair, although little of it is visible beneath the cowl, and wears glasses. When her glasses come off- whether she removes them or they are forcibly knocked off- Yumie "wakes up". Yumie prefers to remove the nun's cowl, keeping the scarf around her neck and letting her hair flow free. Yumie also has slightly narrower eyes and usually can be seen with a maniacal grin. She also carries her katana, holding the sheath in one hand and the blade in the other when in use. She wields the sword in either hand. Yumiko Takagi is noted to be the only Hellsing character stated to be of Japanese ethnicity.
In Hellsing chapter 74 Relics, she attacks Walter, enraged after seeing him desecrating Father Anderson's remains. Although moving extremely swiftly, she is outmatched and cut into pieces by Walter's wires. Heinkel is hysterical and aims her guns at Walter, only to be shot and wounded by The Captain. Yumie makes a full appearance in OVA V.
She knows various sword drawing techniques and is adept enough to kill even from outside the room where her victim is, but is quite capable of smashing men's heads into walls with her bare hands as well. Yumiko has commented how hard it is for her to "get Yumie to sleep" after she has been provoked into action. Usually, Yumiko and Yumie switch control over her body when Yumiko's glasses come off, or when either is knocked unconscious. Heinkel uses this technique to awaken the latent Yumie and have her brutally kill several terrorists in the first volume of the manga extra Crossfire feature.
- The character of Yumie originally appeared in Crossfire as the violent other identity of Yumiko Takagi, a bespectacled and pacifist nun. Despite nearly identical character traits, the Yumie in Hellsing and the Yumie/Yumiko of Crossfire are two entirely separate characters, as Crossfire is a separate story and not part of the Hellsing canon, because Enrico Maxwell looked too much like Integra.
- Yumiko's prototype was in Kouta's old works Hi-and-Low along with Integra.
- Despite being confirmed for being of Japanese descent, the English Dub of the OVA gives her a Welsh accent, though this may be because of an upbringing in a European country.
- The Japanese characters for "Yumiko" (由美子) and "Yumie" (由美江) differ only on the last syllable. Many people tend to make the mistake of Yumie "Yumee", pronounced with two syllables, instead of the correct name, "Yum-ee-eh" (three syllables). Yumi (由美), Yumiko (由美子) and Yumie (由美江) are all different names. Yumi, however, forms base name for both Yumiko and Yumie. Yumi, as written, is composed of the kanji for "Significance/Reason" and "Beauty". The name 'Yumiko' adds the character for "Child" to the end (子 ko) — which seems to be metaphorically symbolic of Yumiko, who is more innocent and childlike than violent Yumie. The name Yumie adds the character for "Inlet" (江 e).