Well, this is an unexpected development. You'd envisioned several scenarios, including a bloody fistfight that ended with her flying out the window and vowing to get you next time and one where she summoned physical representations of your many, many inner demons and you both destroyed her and grew as a person.
Her letting you kill her was not on the list.
You procrastinate for a few seconds, twirling your bayonets, before sighing and putting them back up your sleeves. "Well," you say, "shit. It'd be like killin' a puppy now, and not the toothy kind what eat yer socks." You shake a metaphorical fist at the memory of Mr. Winston, who devoured many an unattended piece of laundry and piddled in countless inconvenient spots.
Ebrietas raises her head ever-so-slightly to face you.
If your brain wasn't weird, you would have died when I tried to talk to you. I was willing to let that happen.
"Why, exactly? Can't rightly judge ye for that without knowin' why."
I was sad and angry because I killed Allison. I wanted to talk to someone so much I didn't care what it would take anymore.
You shrug. "So ye got angry and ye lashed out. I do that, too."
"He does," confirms Eileen. "It's quite a sight."
Ebrietas tilts her head slightly. You could have died, though.
"But I didn't, did I? Look, if ye really think ye deserve ta die, stand up and fight me, 'cus this ain't sportin.' If ye just feel bad, then let's talk."
The poor thing looks so confused. You're actually somewhat amazed at the efficiency with which she utilizes her limited facial features to convey emotion. Really?
"If losin' yer head and gettin' violent was enough by itself ta make me kill ye, I'd be a very lonely man." You think back to some of Heinkel's tantrums. Maybe giving her pistols at the age of five was a wee bit premature.
Ebrietas straightens up somewhat and slithers over to you, her massive head blotting out a good portion of the incoming moonlight. What do you want to talk about?
"I think we got off on the wrong foot. Tentacle. Anyway, let's start from the beginning; I'm Alexander Anderson of the Catholic Church, and she is Eileen, Hunter of Hunters."
I'm Ebrietas.
"Is that yer real name?"
I don't think you could pronounce my real name.
"You sure?"
How many of those red flappy vocal organs do you have? I estimate that you'd need at least four.
"Point taken. Let me find somewhere more comfortable."
You look around for a dry spot and prompt Eileen to do the same. You find a decent-sized statue on its side, its upper portion almost entirely out of the water, and seat yourselves.
"Are we really doing this?" Eileen whispers.
"Everyone deserves a chance."
Ebrietas' anatomy being nonconducive to sitting, she simply relaxes somewhat, resting a portion of her bulk on her lower tentacles.
"Now," you say, "how's about ye tell us yer story? If ye still want ta die when ye're done, then at least we'll all be nice and rested for the fight."
Are you sure? I've been alive a really long time. I could try to transfer the information directly into your minds.
"How confident are ye that it won't make our brains dribble out our noses?"
...A little?
"Let's just talk, then. Some things are worth takin' time for."
And so, in the middle of a monster-ridden hellscape, not far from the scene of several massive battles between you and the forces of evil, sitting next to an elderly woman who is the human equivalent of a butcher shop in a category-five tornado, you talk with Ebrietas.
I was with the others when they made contact with the people of Pthumeria.
"How do ye even spell that?"
I'm still not very good with letters, but I think there's a 'P' in front. Your language is stupid.
"I know, right?"
She really has been alive for a really long time. Swishing her tentacles idly through the waters, she explains the fall of Pthumeria, the other Great Ones leaving her behind, creating the phantasms in a desperate bid for companionship, and many more marvels of her centuries-long life.
You notice that the moonlight doesn't change throughout her story.
When the Byrgenwerth scholars found me, I was so excited I accidentally killed three of them trying to tell them how happy I was. The others kept their distance after that, except for Master Willem. Master Willem tried really hard to learn how to communicate with me. Then I remembered Pthumeria, and I decided to give them my blood. They were all excited and for a while they were all nice to me. Then Master Willem started arguing with Laurence.
I don't know what they were arguing about, but one day Laurence decided to leave and he asked me to go with him. Master Willem got mad but he said I should do it.
"So how did ye get here, exactly?"
I flew.
"You can fly with those things?"
I can! she chirps, and hovers momentarily to demonstrate.
"How does that work?"
The fundamental physical forces of this dimension are actually incongruous with those of my home dimension, allowing for my kind to perform feats that are impossible for local residents.
"Ah."
She explains how the Grand Cathedral was essentially built around her, keeping her close to the people of Yharnam she thought her blood was helping.
They told me they were just going to study my blood, and they said they'd found a way to heal people with what they learned. I wanted to ask them more about it but they got angry if I asked too many questions and I didn't want them to leave me. Allison was the only one who would spend time with me, but even she wouldn't tell me everything that was going on.
Ebrietas' tentacles still for a moment, then hang loosely from her sides.
Allison said she wanted to be able to talk with me. I could understand the language and give yes/no answers at this point, but she wanted to communicate for real. She wanted me to make her into something that I could speak with. I tried.
You don't know how much time has passed. You're not sore from sitting on the rough stone, but she's given you quite a bit of information to sift through. When nothing further is forthcoming, you get to your feet.
"So how do ye feel now? Still want me ta kill ye?"
I don't know.
"What do ye want?"
I don't know.
[] Write in...
Really? The first thing that comes to your mind is this and not... 
on that?