Privacy Policy

App: Byosoku Diary / Effective: September 22, 2026 / Last updated: September 22, 2026

Byosoku Diary (the "App") is a diary app provided by misoclub ("we", "us"). We respect the privacy of everyone who uses the App, and this Privacy Policy (the "Policy") explains how we handle information.

The App has no feature for sharing diaries or photos with other users. What you write and the photos you attach are for you alone. We use the cloud (Google Firebase) only to keep a copy of your own data so that it survives a change of device and stays in sync across your devices.

1. Accounts (anonymous authentication and optional account linking)

To back up and sync your data, the App uses Firebase anonymous authentication to assign each user a random, anonymous identifier. No name, email address or phone number is required at this point, and we do not collect any.

If you want to move your data to a new device or restore your account, you may optionally link a Google or Apple account. When you do, we receive the email address and display name provided by that account and store them in our cloud database (Cloud Firestore) to identify the linked account, to support you and to restore your data. Linking is optional; the App works without it.

If you choose "Hide My Email" with Sign in with Apple, Apple's private relay address is used instead. You can link an account at any time from Settings, and "Delete all data" (below) also unlinks it.

2. Information stored on your device

What you record — diary text, dates and times, notebook names and covers, attached photos, and your notification, theme, wallpaper and font settings — is stored on your device. Photo files live in the App's own private storage area and are not exposed to other apps.

Your app-lock passcode and biometric setting are stored only on your device and are never sent to the cloud, nor included in any export or backup.

3. Information stored in the cloud

For backup and device migration, the following is stored in our cloud (Cloud Firestore and Firebase Storage) in an area only you can read and write. It is never made visible to other users.

There is a limit on how many photo bytes can be stored in the cloud (100MB on the free plan, 2GB with Premium). Photos beyond that limit stay on your device but are not uploaded.

When you delete a photo or an entry in the App, the corresponding cloud data is deleted as well. To guard against accidental deletion and failures, deleted image files are retained by our storage provider's soft-delete feature for up to 90 days before being permanently erased. This is an operational safeguard; the App itself offers no "undo".

4. Push notifications

Reminders to write are local notifications generated on your device. Separately, we use Google Firebase Cloud Messaging (FCM) to deliver announcements from us, and store a per-device notification token for that purpose. You can turn notifications off in Settings.

5. Advertising

The App uses Google AdMob to serve ads. AdMob may collect and use an advertising identifier (Advertising ID / IDFA on iOS) and device and usage information to deliver ads, prevent fraud and measure performance. Google's handling of this information is governed by Google's privacy policy.

Whether ads are personalized depends on your consent. On iOS, the App asks for tracking permission (App Tracking Transparency). If you allow it, personalized ads using the IDFA may be served; if you do not, ads are non-personalized. Either way, every feature of the App remains available. In regions such as the EU/EEA, we display Google's User Messaging Platform (UMP) consent form and follow your choice.

The App offers an auto-renewing subscription (in-app purchase) that removes banner ads and raises limits. Purchases and payments are handled by the App Store (Apple) or Google Play (Google); we never receive or store your credit card or other payment details.

6. Crash reports and usage statistics

To improve quality, we receive crash information (where the crash occurred, device model, OS version, app version) through Firebase Crashlytics, and statistics such as screen views and feature usage counts through Firebase Analytics. The contents of your diary entries and photos are never included.

7. Third-party services

The App uses the following services:

Their handling of data is governed by their own privacy policies (Google: https://policies.google.com/privacy, Apple: https://www.apple.com/legal/privacy/).

8. Contacting us and reporting

If you contact us from the Settings screen, we receive your message, any contact address you choose to provide, any image you attach, and the app and device information needed to help you (app version, OS and platform, language settings), and use them to provide support. You can also report inappropriate content or display problems in the App from Settings.

9. Disclosure to third parties

Except as required by law, we do not provide your information to third parties without your consent. The services listed above act as our processors and handle information under our instructions.

10. Deleting your data

"Delete all data" in Settings deletes the data on your device and the data stored in the cloud (including photos and linking information), and releases the linked Google/Apple credential. If you only sign out, on-device data is erased while the cloud copy remains, so signing in again with the same account restores it. Uninstalling the App erases the data on your device.

11. Children's privacy

The App does not knowingly collect information from any specific age group. Children should use the App under the supervision of a parent or guardian.

12. Security

We take appropriate measures to protect the information we collect and store against loss, leakage and damage. Cloud data is protected by access rules that permit reads and writes only with the owner's own credentials.

13. Changes to this Policy

We may revise this Policy as needed. Significant changes will be announced on this page, and the revised Policy takes effect when posted here.

14. Contact

For questions about this Policy or the App, please contact us: