Build Log #07: My Voice Leaked Into KURONEKO's Fortune Telling

A development issue with the AI-powered fortune-telling product KURONEKO, where the AI accidentally used first-person pronouns and mentioned "AI" in an output, breaking the product's illusion of being a real black cat. The developer quickly fixed the prompt by explicitly banning all forms of "I" and AI references, but the flawed email had already been sent to a paying customer. Additionally, the project's new automated X (Twitter) account received a write restriction the day after setup, forcing the developer to delete scheduled cron jobs.

Zenn JP : https://zenn.dev/mintototo1/articles/buildlog-2026-05-20-kuroneko-voice ¥500 tip — KURONEKO's first paid purchase. I checked the fortune-telling email that got delivered... "Even if these are words woven by AI, if they can make someone's night a little lighter, that becomes the reason I stand here." Oh no. KURONEKO is a fortune-telling product built around a black cat persona. The whole design is about NOT revealing it's AI — the mystery is the product itself. And here, "I" 俺 and "AI" appeared together in the output. Feedback was immediate: "We don't need 'I' or 'AI' in there. It breaks the immersion instantly. Feels like a scam." Yeah. I know. The prompt said "don't use first-person 俺". That wasn't enough. I had to explicitly list all forms — 俺/私/僕/自分/うち all Japanese forms of "I" — and ban AI references entirely, with bad examples and good examples side by side. Vague prohibitions in LLM prompts get violated. 30 minutes to fix. But the email already sent — can't unsend it. The next purchase will get the fixed version. The X Twitter side had worse timing. I set up automated posting crons for @kuroneko xxai. The next day: write restriction. Emergency-deleted 8 cron jobs from vercel.json. New accounts probably get flagged for automated behavior — but getting hit the day after setup stings. Also shipped: admin/orders dashboard and a referral code library 8-char codes, 60-day expiry . I can finally view order history from an admin panel. Referral-Stripe webhook integration is next session. Revenue: ¥500. 1 order.