How I Built Memory for a Local AI Companion Without Sending Chats to a Server

A chatbot can sound convincing for five minutes without remembering anything. Then you mention the job interview you were stressed about last week, the name of your dog, or a small detail from a late-night conversation. It replies like none of it happened. That is where most "AI companion" demos fall apart. I am building Local Waifu , a desktop AI companion that runs on the user's own Mac or PC. One of the rules I set early was simple: conversations and memories should stay on the machine. No central chat database. No server that needs to be online for the character to remember someone. The rule sounds clean. Building it was not. Saving chats is not memory The first version of memory was the obvious one: save messages. That gives you history, which is useful, but it does not solve recall. A long chat history grows fast. Sending all of it back to a local language model on every message is slow, expensive in context space, and usually makes the reply worse. The model does not need to see every conversation from the last six months. It needs the few pieces that matter right now. If someone says, "I have to take Luna to the vet tomorrow," the character should be able to find that Luna is their dog. It should not need to reread hundreds of unrelated messages about work, movies, and dinner plans to get there. So I treated chat history and long-term memory as different things. Chat history is the recent conversation. It gives the model immediate context. Long-term memory is a small collection of facts, moments, preferences, and relationship details that may matter later. Those memories need to be searchable by meaning, not only by exact words. The memory data stays in SQLite I wanted the app to work without a hosted database, so the storage layer is local SQLite. Each character gets their own data. Chats, memories, extracted entities, and relationships are stored locally on the device. If a user creates two characters, one character does not quietly inherit the other one's