A woman of pleasure whose blood might be more than it seems.
The NPC Arianna is found in a dark alley in Cathedral Ward. Her door is across from the Skeptical Man window. If you speak to her, you can tell her a safe place to go. If you wish her to live, send her to the Chapel.
Once she is there, you can obtain her blood. Be mindful of who else is around though. If you also saved the Nun Adella, then she will get mad at you for using her blood, and if you continue to use it, she will kill Arianna.
If Arianna lives until after you kill Micolash, Host of the Nightmare, then she will to a room below Oedon Chapel just before the Cathedral Ward lamp. She will give birth to a Celestial Child there, and if you kill it, you will obtain One Third of Umbilical Cord.
Her shoes are described as "Innocent and cute, in contrast with its owner."
Future Press game guide description: "A prostitute residing in one of the Cathedral Ward's darker corners. Arianna is a living testament to the old adage. "Beauty is only skin deep." Her elegant appearance belies a personality as blunt as a bludgeon, and her very blood bears striking similarities to that which was once forbidden by the Healing Church."
Arianna is a prostitute or “woman of pleasure” residing in the Cathedral Ward of Yharnam. It seems she is considered to be of very low social standing in the society of Yharnam, though evidently not as low as the blind beggar, who even she does not seem to take into consideration when she calls herself a “black sheep” of the survivor group in Oedon Chapel. The Chapel Samaritan will tell you that Arianna actually talks to him, even though she doesn’t mince words. Because of this he believes her to be a “good woman” and she certainly does stand out from the rest of the Oedon Chapel survivors. Each time you talk to the Samaritan after bringing a new survivor in, his dialogue will tell you that none of them ever bothered to thank him or even talk to him, Arianna is the exception.
The Bigoted Old Man will tell the player that Arianna is jealous and resentful of the blood of Adella, Nun of the Healing Church, and yet through Adella’s actions it becomes apparent that it is the other way round (see Adella’s page for details).
So what is so special about Arianna and her blood? Arianna’s dialogue when giving her blood indicates that her services include provision of her blood to customers. She tells the player that it isn’t her first time giving blood, implying this must be one of the ways she makes a living. Her vial of blood describes it as being similar to precisely what was once forbidden by the Healing Church. Her Noble Dress traces back to the bloodline of Cainhurst and therein lies our answer. Arianna is heavily implied to be a descendant of the Cainhurst nobles. Her dress is likely to have been inherited throughout the years, and her hair is light, though suitably a ‘tarnished’ blonde in comparison to the greyish silver hair that defines the Cainhurst line, as seen with both Queen Annalise and Lady Maria.
Arianna is certainly aware that her blood is special, why else would she offer it to you or have offered it to others before? Adella is actually aware of the nature of Arianna’s blood. She will tell the player, after they have drunk enough of Arianna’s blood that it is “tainted” and that she can’t help desiring it. After the player kills Rom, the Vacuous Spider the ritual conducted by the School of Mensis is revealed and the red moon (or Paleblood) hangs low. A note in Byrgenwerth reads: "When the red moon hangs low, the line between man and beast is blurred. And when the Great Ones descend, a womb will be blessed with child. It is at this point in the night that Arianna begins to experience stomach pain.
It is revealed later on in the game’s events that Arianna’s pains were in fact cramps and that she has fallen pregnant to what appears to be a Great One. But how could this even happen? We know that the blood of Cainhurst is special, and that it is sought out by many parties. But there is one party in particular that stands out from others in this situation. The Oedon Writhe and Formless Oedon runes tell us that the oozing blood is a medium of the highest grade, and the essence of the formless Great One, Oedon. Both Oedon and his inadvertent worshipers surreptitiously seek the precious blood. This is very interesting considering Adella’s comments that she can’t help but seek Arianna’s blood, and the fact that the Oedon Writhe rune is found etched in her mind. The One Third Umbilical Cord also tells us that every Great One loses its child, and then yearns for a surrogate, and Oedon, the formless Great One, is no different. To think, it was corrupted blood that began this eldritch liaison. All this seems to indicate that Oedon seeks precious, rare blood, and we know that Arianna has precious and rare blood. Adella’s actions indicate that Oedon in fact seeks Arianna’s blood and where is it that Arianna resides for most of the night? Oedon Chapel.
Oedon is a formless Great One, perhaps capable of impregnating Arianna without her knowing, certainly his presence can go undetected since he is formless and exists in voice only. Arianna certainly indicates that she doesn’t know what’s going on, only saying she's "a bit out of sorts" and that there’s “something wrong with me…” when going through labour. Then after she gives birth to the Celestial Child, which are supposedly the product of Great Ones impregnating human women, she will exclaim that “it can’t be” and that it’s a “nightmare”. If you kill the Celestial Child, it will also kill Arianna, implying there is a deep connection between them. Arianna’s Celestial Child will also drop the One Third Umbilical Cord with the description of Oedon and his goals, all but confirming that Oedon impregnated Arianna.
Arianna’s fate prior to coming to Oedon Chapel perhaps gives us a clue as to the what happened to the nobles of Cainhurst that survived Logarius and his Executioners. It seems that they may have fled with nothing but the clothes on their backs and attempted to ingratiate themselves into the Yharnam population. But perhaps the stigma of light hair, or their blood (since even Adella seems to know about Arianna’s bloodline) caused many of them to be on the fringes of society. Arianna does reside in the Cathedral Ward, so perhaps she or her family were able to find some success. More likely though, the Church could have housed her there as a way of keeping an eye on her, and abusing her as a source of forbidden blood.