Privacy Policy

Last updated: October 23, 2026

Mainichi is an app to study kanji and Japanese vocabulary. Rota Studio makes it (“we”, “us”). This policy tells you what data the app and this website collect, why we collect it, and what you can do about it.

• You can use Mainichi with no account. Your progress then stays on your device.
• An account is optional. It keeps your progress in sync on all your devices.
• No ads, no tracking and no analytics tools. We do not sell or share your personal data.
• You can delete your account and its data in the app at any time.

Without an account

Your progress (your reviews, your cards and your settings) stays in the app on your device. We do not receive it. When you practice writing, the app checks your drawing on the device. It does not keep the drawing, and it does not send it anywhere.

The app sends crash reports, which do not identify you (see Crash reports).

With an account

You can make an account with an email address and a password, with Sign in with Apple, or with Sign in with Google. The account keeps a copy of your progress, so you can study on more than one device and get your progress back on a new device. We keep:

• Account data: your email address, and your name if Apple or Google gives it to us. Sign in with Apple lets you hide your email address: Apple then gives us a private relay address. Sign in with Google also gives us a link to your Google profile picture, which we do not use. For a password, we keep only a secure hash, never the password itself.
• Study data: for each review, the kanji or word, the type of card, your grade, the state of the card, the time of the review, the time that you took to answer, and the time zone offset of your device. Also your app settings, for example your daily limits, your course, your theme, and the scheduling parameters that the app tuned to your memory.
• Security records: our server provider records sign-ins and requests, with the time and the IP address, to keep the service secure and to find faults.

We use this data only to run your account and to sync your progress. To confirm your email address or to reset your password, we send you an email with a code. We send you no other email.

Crash reports

When the app crashes, freezes or shows you an error, it sends a report to Sentry, our error-monitoring provider. A report holds:

• the error, and the place in the app’s code where it happened;
• the app version, the device model, the iOS version, and the language and time zone of the device;
• the state of the device, such as free memory, low-power mode and its thermal state;
• a short list of app and device events before the error, such as the app going to the background or a low-memory warning.

A report does not hold your name, your email address, your account ID, or an ID of your device or of the app’s install. It has no screenshots, and no list of your taps or of the screens that you opened. Sentry does not store your IP address or a location from it. We use the reports only to find and fix bugs. Sentry deletes them after 90 days at most.

If you turn on Share With App Developers in the iOS settings (Privacy & Security → Analytics & Improvements), Apple also gives us its crash reports and usage statistics of the app. Apple controls that choice, under its own privacy policy.

Purchases

Apple handles every purchase in the app through the App Store. We never see your payment details. The app gets from Apple only which purchases are active.

Our service providers

These companies run parts of Mainichi for us. Each one is bound by contract to use your data only to provide its service to us, and to protect it as well as this policy does:

• Supabase: the account and sync servers. Your account and study data are stored in the United States (Ohio).
• Resend: sends the emails with your codes.
• Sentry: receives the crash reports, in the United States.
• Cloudflare: hosts this website, and forwards the email that you send to support@mainichi.co.

When you use Sign in with Apple, Sign in with Google or the App Store, Apple or Google does that step under its own privacy policy, and gives us only the data that this policy names.

We do not sell your personal data, and we do not share it for advertising. We give it to nobody else, unless the law requires it.

Tracking

Mainichi does not track you across other apps or websites, and it lets no third party do so. So the app and this website work the same way when your browser sends a Do Not Track signal.

This website

mainichi.co sets no cookies and uses no analytics. Cloudflare, which hosts it, processes your IP address to deliver the pages and to protect the site from attacks.

How long we keep data

• Account and study data: until you delete your account. Then we delete them from our database at once.
• Security records, email logs and backups: our providers delete them on their own schedule.
• Crash reports: 90 days at most.
• Email that you send us: as long as we need it to answer you.

Delete your data

• Your account: in the app, open Settings → Account → Delete account. This deletes your account and all its study data from our servers, and erases your progress from the device. For Sign in with Apple, it also revokes the app’s access to your Apple Account. For Sign in with Google, the app disconnects from your Google account.
• The device: Sign out erases your progress from the device. It stays in your account. Without an account, delete the app to remove all its data.
• You can also ask us by email to delete your data.

Your rights

Where you live can give you rights about your personal data, for example in the EU, the UK or California: to see it, to get a copy, to correct it, to delete it, and to object to or limit its use. To use these rights, email support@mainichi.co. We can ask you to show that the account is yours. We answer within 30 days. You get the same service when you use your rights.

EU and UK: we process account and study data to give you the service that you asked for (a contract). We process crash reports and security records for our legitimate interests: to keep the app stable and secure. You can complain to your local data protection authority.

California: we collect identifiers (email address, name, account ID), internet activity (security records with IP addresses), and app data (study data, settings and crash reports), for the purposes above. We get this data from you, from the app on your device, and from Apple or Google when you sign in with them. We do not sell or share personal information, as the CCPA defines these words, and we do not use sensitive personal information.

Transfers

Our providers store data in the United States. If you live in another country, your data goes to the United States. Our providers protect these transfers with the safeguards that the law requires, such as the EU Standard Contractual Clauses.

Security

All data travels encrypted (HTTPS). Our database lets each account read only its own data. No system is perfectly secure, but we take reasonable steps to protect your data.

Children

Mainichi is not made for children under 13. We do not knowingly collect personal data from children under 13, or under the minimum age in their country. If you think that a child gave us personal data, contact us and we delete it.

Changes

When we change this policy, we post the new version on this page and change the date at the top.

Contact

Rota Studio · support@mainichi.co