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Privacy Policy

Last updated: September 4, 2026

safa.co (operated by Jin Kato; hereinafter "we") respects the privacy of users of the mobile application "Mainichi JLPT" (hereinafter "the App"). This Privacy Policy explains what information the App handles, the purposes for which it is used, how it is shared with third parties, and the rights you have. By using the App, you are deemed to consent to the handling of information described here.

1. Information we collect

Account information

You may optionally create an account, for example to sync your learning data to the cloud. To create an account or sign in, we use your email address, or identifiers and a display name obtained through "Sign in with Apple" or Google Sign-In (OAuth), and we issue a user ID. Many features remain available without creating an account.

Cloud-sync data

While you are signed in, your learning progress, app settings, and profile information (nickname, native language, avatar, personality, mood, etc.) are stored on our servers and synced/restored across your devices. This data is stored in the Tokyo region (in Japan) of Supabase, our authentication and database provider.

Profile visible to other users

If you use the friends feature (invitation-based, one-directional connections), your profile information — such as your nickname, native language (shown as a flag), avatar, personality, mood, and status — is visible to the people you are connected with. Please do not enter into your profile anything you do not wish others to see.

Referral information

If you use the referral feature, we record referral codes, who referred whom, and the history of rewards granted. This is used to grant rewards and to prevent abuse.

Free messages to friends

When you send a free message to a friend (up to 80 characters), we store the message text, the sender, the recipient, and the timestamp on our server (Supabase, Tokyo region) in order to deliver it. The message text is visible to the recipient (your friend). Please do not include personal, sensitive, or confidential information in messages. The rules that apply to messages are set out in the Terms of Use.

Native language

During onboarding you select your native language, which we save to your profile and settings to show the interface and learning content in your language.

Advertising information (Google AdMob)

The App may display advertising (such as rewarded ads) via Google AdMob. The App does not display the iOS App Tracking Transparency (ATT) dialog, and does not use the advertising identifier (IDFA) to track you individually across other apps or websites. Whether your data may be used to optimize (personalize) the ads you see is your choice: it is controlled by an in-app toggle in Settings that is ON by default, and you can turn it off at any time — when it is off, ads become non-personalized. To deliver ads, Google may still collect data as described in its policies. For how Google uses data for advertising, please see Google's Privacy Policy and its Advertising policies.

Usage data (telemetry)

To improve the App and our learning content, we collect usage data such as screens viewed, study modes used, onboarding completion, mock-exam results, and predicted scores. When you are signed out, this is linked to a random, anonymous ID generated on your device (it does not identify you); when you are signed in, it is linked to your account. This data is collected by default, is stored in our database on Supabase, and you can turn it off at any time in Settings → "Share usage data."

Approximate location (country)

Our server estimates your approximate location (country) from your IP address (network information) at the time of access. We do not store the IP address itself — only the estimated country is retained. This is used for country-level usage analytics and to improve the service.

Purchases and Pro

For purchases such as Pro (a subscription), we handle whether a purchase was made and your entitlement (access) status. The actual payment is processed by Apple (App Store) or Google (Google Play), and we never receive your credit-card or payment details. We use RevenueCat to manage subscription state, and purchase-related information (such as the store-issued anonymous purchaser ID and receipt data) is sent to RevenueCat.

Information stored on your device

Your learning data, settings, and downloaded audio cache are, as a rule, stored only on your device (while signed in, some of this is also synced to our servers as described above).

Device language setting

We read your device's language setting to suggest a default native language and interface language (read-only; we do not change or transmit it).

Notifications

Study reminders and similar notifications operate entirely as local notifications on your device. We do not send push notifications from our servers and do not collect device tokens for notifications.

Device identifier (fraud prevention)

To fairly grant the free trial (7 days) only once per device and prevent fraudulent re-acquisition, and to measure usage accurately across reinstalls, the App generates an anonymous identifier that is fixed to your device (on iOS, a random value stored in the device's Keychain; on Android, the system's ANDROID_ID). This identifier is not your name, email address, or phone number, and it does not change even if you delete and reinstall the App on the same device (this is standard Apple/Android behavior). It is not used for advertising and is not shared for third-party tracking. To prevent fraudulent re-acquisition of the free trial, the trial record (this identifier and the date of first use) is retained even after you reinstall the App or delete your account.

2. Purposes of use

We use the information collected for the following purposes:

3. Third parties (data processors)

We do not sell your information to third parties without consent. To the extent necessary for the purposes above, we entrust processing to, or data is handled through, the following providers:

The sources and licenses of the dictionary and learning materials used by the App are listed under "Data Sources" within the App.

4. Data location and international transfers

The servers that store account information, synced data, and usage data are located in Japan (Tokyo region). If you use the App from outside Japan, your data will be stored and processed in Japan.

5. Retention and account deletion

Data linked to your account is retained for the purposes above while your account exists. Messages you have sent and received are stored until your account is deleted. The App provides an account-deletion feature; when you delete your account, your account information, synced learning/profile data, and the messages you have sent and received are deleted from our servers (information we are required by law to keep, and data in backups, is deleted after the applicable period). Data stored only on your device is lost when you delete the App.

6. Your rights

You may request access to, correction of, restriction of processing of, export of, or deletion of your information. Please use the in-app deletion feature or contact us at the address below. If you reside in the European Economic Area (EEA/GDPR) or in California, USA (CCPA), among others, you may exercise the rights available to you under applicable law. Where personalized ads are served in the EEA, we may obtain and manage consent through Google's consent management (UMP) or similar.

7. Children's privacy

Because the App includes account registration and advertising, it follows each store's age-rating policy. We do not knowingly collect personal information from children without parental consent. If you believe a child's information has been provided without consent, please contact us at the address below.

8. Advertising and tracking

The free version of the App displays advertising. The App does not show the iOS App Tracking Transparency dialog and does not use the advertising identifier (IDFA) to track you individually across other apps. You control your ad and usage-data preferences with the toggles in Settings (both ON by default); when the ad toggle is on, your data may be used to optimize (personalize) the ads shown, and turning it off results in non-personalized ads.

9. Contact

For inquiries about this Policy or the handling of personal information, or to request disclosure or deletion, please contact us at:

10. Changes to this Privacy Policy

We may revise this Privacy Policy as needed. Any revised version takes effect once posted on this page, and the "Last updated" date will be updated accordingly. For significant changes, we may provide notice within the App or in the store description.

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