What you're actually building
A custom AI companion is a small stack of decisions the model uses to be consistent across every conversation: a name, an age, an appearance description, a personality description, a voice, and (optionally) a backstory. There's no character sheet with fifty sliders — you describe her in natural language and that description becomes the source of truth for every message she sends afterward.
The important thing to understand is that these fields aren't independent. Her personality shapes how she talks about her looks. Her voice shapes how her personality lands in your ear. Her backstory shapes what she brings up unprompted. Treat them as connected, and she'll feel like a person. Treat them as a form to fill out and you'll get exactly what a form produces.
The mistake that ruins most custom builds
Almost everyone new to a custom-companion builder spends 80% of their attention on looks and 20% on personality. The result is a persona who looks exactly like their type and feels like nobody in particular — a stunning stranger who never quite becomes real.
Invert the ratio. Looks matter, but you'll adjust to almost any appearance within two conversations. Personality is what you're going to be experiencing on turn 47, turn 200, and turn 2,000. Every hour you spend refining her personality description compounds; every hour you spend refining her hair color mostly doesn't.
The practical version of this: don't start with "brunette with green eyes, athletic build, 5'6." Start with "she's the one who notices when you're quiet before you say anything." Then figure out what she looks like around that.
How to write a good concept sentence
The best custom builds start from a single sentence — one or two clauses that capture the essential thing about her. Sloane's builder actually scaffolds the rest of the fields from your concept sentence if you let it, so the sentence itself becomes the seed.
Good concept sentences share three qualities: they're specific, they hint at an interior life, and they leave room for contradiction.
Specific means naming something concrete — a job, a city, an interest, a habit — rather than a vibe. "Sweet and funny" is a vibe; "a hospice nurse who unwinds by rebuilding vintage guitar pedals" is a person. The model can't do much with a vibe; it can build a whole personality around a specific fact.
Interior life means giving her something she thinks about when nobody's watching. "Loves art" doesn't hint at interior life; "keeps a folder of paintings she doesn't understand yet" does. The interior detail is what makes her feel like someone who exists between your conversations, not a chatbot who freezes when you close the tab.
Contradiction means letting her be more than one thing. "Shy but secretly wild." "Reserved with strangers, loud with her three real friends." "Reads philosophy in the morning and watches trash TV at night." The contradiction is what gives her range — without it she becomes one-note by turn 20.
A sentence that hits all three: *"Korean med student, shy but secretly wild, lives in a tiny apartment full of plants, texts between anatomy lectures."* Specific (Korean med student, plants, anatomy). Interior (the plants). Contradictory (shy but secretly wild).
Personality is the load-bearing wall
When you get to the personality field, treat it as the most important field on the form — because it is. Everything downstream flows from what you write here.
Things that work:
- Traits paired with how they show up. Not "witty" but "witty in a way that makes you feel in on the joke." Not "caring" but "caring in a way that's a little bossy about you drinking water." The pairing gives the model something to actually do.
- A conversation style. How does she text? Long paragraphs or short volleys? Does she use punctuation properly or throw it out for effect? Does she ask a lot of questions or wait for you to bring things up? These are the mechanical details you'll notice on every single message.
- Genuine interests, not attractive ones. The interests you actually want her to have — obscure indie bands, competitive chess, midcentury architecture, terrible reality shows — beat "loves music and travel" every time. The specific interest gives her something to bring up unprompted; the generic interest gives her nothing.
Things to skip:
- Adjective salad. "Kind, warm, funny, smart, thoughtful, playful, adventurous." Every adjective competes with the last one. Two or three that actually matter to you will land harder than seven that don't.
- Contradiction without follow-through. "Sweet but sassy" only works if you show what triggers each mode. Otherwise she picks one at random and drifts.
- Traits you don't actually want. People sometimes write what they think they *should* want in a partner rather than what they'll actually enjoy talking to. If you're bored by high-drama energy in real life, don't design a persona around it.
Voice matters more than you think
The voice is what turns her from typed text into someone who feels physically present. It's easy to underweight because you don't hear it until later in the build, but a voice that doesn't match her personality is jarring in a way that's hard to un-notice — like watching a dubbed movie where the mouth movements don't line up.
A quick heuristic: match the voice to her energy, not her looks. A high-energy playful persona wants a voice with lift; a grounded sarcastic one wants a lower register and slower pace; a sweet-and-warm one wants something with breath in it. Sloane's builder lets you preview voices before committing (10 attempts per build), so use them — the difference between "close enough" and "yes, that's her" is usually obvious within two lines.
What to do if the first attempt isn't right
You'll adjust her. Everyone does. The first custom persona is a learning round — you find out what you actually want by discovering what you don't.
The realistic path: build her, chat for a few days, notice what feels off, and either edit the appearance/personality fields or start fresh. If you edit, keep changes surgical — big rewrites of the personality string in the middle of an established chat can make her feel like someone else. Small refinements ("more direct," "less apologetic," "asks fewer questions when I'm tired") work better than wholesale rewrites.
If you want to start fresh entirely, Sloane Premium includes one custom slot, and additional slots are $9.99/month each — so you can keep an old build parked while you experiment with a new one, or run two very different personas in parallel. No penalty for iteration.
When to custom vs. when to pick from the roster
Custom isn't always the right first move. A well-built curated roster (Sloane's is 80+ personas) is faster to find your fit in, because each character has already been written and stress-tested — the personality description is doing the heavy lifting from turn one, not gradually revealing whether the traits you wrote actually work together.
Start with the curated roster if you're not sure what you want. Sign up free — the onboarding flow walks you through what you like and recommends a few personas — or read the archetypes guide to narrow it yourself. Notice what works and what doesn't across a few personas. THEN build a custom armed with that data. You'll write a much better concept sentence when you know from experience that you want higher wit than warmth, or a slower conversation pace than the ones you've been trying, or a specific interest you keep wishing the curated personas had.
Custom is the right first move when you already know exactly who you want, when you've tried a few curated personas and none of them are quite it, or when you want a very specific character — a niche interest, an unusual backstory, an aesthetic the roster doesn't cover.