Hibiki has one user: its owner. Nobody else's data is collected.
With the owner's consent, Hibiki asks Google only when the owner is free or busy (the calendar.events.freebusy scope), to pick a time for one daily study reminder. It never reads event titles, descriptions, places or guests. It keeps the sign-in token Google issues for this, and does not store calendar data. Access can be removed at any time at myaccount.google.com/permissions.
The owner's flashcards and the things they save are stored on this server (Cloudflare) and sent to Anthropic's API to suggest and fix cards. Nothing is sold, shared or used for advertising.