Sumi: Privacy Policy

Last updated: 23 October 2026

Sumi is a Japanese kanji study app made by an independent developer (Sushil Raj, sushilraj0177@gmail.com). This policy explains what happens to your information when you use it.

The short version

• Sumi has no accounts, no ads, no analytics and no tracking. There is no Sumi server.
• Your progress, settings, letters and saved words stay on your phone.
• The only things Sumi sends over the internet are the requests for Sumi-chan's letters and her voice, and only if you add your own Google Gemini API key. They go directly from your phone to Google, never to the developer.

What stays on your device

Everything you do in Sumi is stored only on your device: your study progress and streak, quiz results, settings, Sumi-chan's letters and your replies, your saved words, recordings of Sumi-chan's voice, her memory notes, and your Gemini API key. The developer cannot see any of it.

Android's own backup may copy Sumi's data (except your Gemini API key, which is excluded) to your Google account, if you have device backup turned on. This is controlled by your phone's settings and Google's policies, not by Sumi.

If you use Settings → Data → Back up, Sumi saves a backup file to the place you choose (for example Google Drive or your phone's storage). The backup never contains your Gemini API key.

Sumi-chan's letters (Google Gemini)

The letters feature is optional. It only works after you paste in your own Gemini API key from Google AI Studio. When Sumi writes a letter or answers one of your replies, it sends a request from your phone directly to Google's Gemini API (generativelanguage.googleapis.com) over an encrypted (HTTPS) connection. The request contains:

• the instructions for Sumi-chan's personality and style that you chose in Settings;
• the name you asked her to call you, if you entered one;
• which kanji you have learned, a few kanji to focus on, and simple progress facts (for example your streak length or that you finished today's lesson);
• a few of your saved words, if that option is on;
• the text of your recent letters and your replies to them;
• Sumi-chan's memory notes (see below);
• today's date, time of day and season, so the letter fits the moment.

The request is made with your own API key, under your own agreement with Google. Sumi asks Google not to store the conversation (store: false), but how Google processes requests is governed by the Gemini API Additional Terms of Service and Google's Privacy Policy. On Google's free tier, Google may use content to improve its products and it may be read by human reviewers, so don't put sensitive personal information in your name or replies.

Sumi-chan's letters are written by AI. They can contain mistakes. Sumi checks every reading against a dictionary on your phone before showing it. You can report a letter from its menu (⋯ → Report this letter).

Sumi-chan's memory

So that she can write like a real pen pal, Sumi-chan keeps short notes as you write to each other: things you've told her in your replies, things she has said about her own life, things she means to ask you later, and a sentence about how close you are. She writes these notes herself, in the same request that writes a letter. They are stored only on your phone, sent to Gemini with each letter as described above, and included in your backups.

You can see every note in Settings → Sumi-chan → What she remembers, delete any one of them, or make her forget everything.

Sumi-chan's voice (Google Gemini)

When Her voice is set to a Gemini voice (Settings → Sumi-chan → Her voice) and you've added your key, Sumi asks Google's Gemini API, with your own key, to read a letter aloud. The request contains only the letter's Japanese text, the voice you chose and a short description of her speaking style. Scheduled letters (and older ones not yet voiced) are voiced in the background, a few a day, so Listen plays at once; chat replies are voiced when you tap Listen.

The audio Google returns is saved on your phone (compressed), so each letter is voiced only once. Recordings are included in your backups, so a restored phone keeps her voice, and are erased when you uninstall Sumi or clear its data. The same Google terms apply as for letters.

If you choose Phone voice, letters are read by your phone's own text-to-speech engine instead, and Sumi sends nothing to Google for it.

Bug reports

If you choose Report a bug, Sumi opens your own email app with a pre-filled message that includes the screen you were on, the item in question, the app version, and your phone model and Android version. Nothing is sent unless you press send in your email app. Emails are used only to fix the problem and are deleted once they are no longer needed.

Permissions

• Internet / network state: only for the Gemini requests described above (letters and voice).
• Notifications: the kanji notification, letter notifications and the daily reminder. You can turn each off in Settings or in Android's settings.
• Vibrate: haptic feedback. Can be turned off in Settings.

Children

Sumi is intended for adults (18 and over). It is not directed at children, and Sumi-chan's letters use the Gemini API, which Google provides only to people 18 and over.

Deleting your data

Everything Sumi stores is erased when you uninstall it, or with Android Settings → Apps → Sumi → Storage → Clear data. Settings → Data → Reset progress clears just your study progress. Your Gemini key can be removed in Settings → Sumi-chan. Backup files you saved are yours to delete wherever you saved them. For anything held by Google under your API key, see your Google account.

Changes

If this policy changes, the new version will be published at the same address with a new date.

Contact

Sushil Raj: sushilraj0177@gmail.com