Privacy Policy

Last updated: July 22, 2026

1. Introduction

This policy explains how Yuji Eto ("we", "us") handles user information in connection with the smartphone app "Sudoku" (the "App").

2. No Account Required

The App does not require sign-up or account creation, and can be used without entering your name, email address, or any other personal information. Puzzle progress (board state, notes, elapsed time, mistake count, etc.) and settings (theme, language, etc.) are stored only on your device and are never sent to us or any external party. The App does not provide any feature to save or sync your play data to a server operated by us.

3. Information We Collect

3-1. Crash and Error Information

We do not collect any information during normal use of the App. The only exception is when the App crashes or encounters an error: in that case, the following information is automatically sent, for the purpose of identifying and fixing the problem, via Firebase Crashlytics, a service provided by Google LLC ("Google").

• Stack trace at the time of the crash or error (internal program information indicating where the error occurred)
• OS type and version
• Device model
• App version
• An anonymous installation identifier (Firebase Installation ID) — a machine-generated ID used to distinguish individual app installations; it is not linked to your name, email address, or any other information that identifies you personally

The crash and error reports we can view in Crashlytics do not include your IP address.

3-2. Information for Advertising

The App displays banner, interstitial, and rewarded video ads through Google AdMob, an advertising service provided by Google. To deliver and measure the effectiveness of ads, AdMob may collect the following information:

• Advertising identifiers (such as IDFA on iOS or the Advertising ID on Android)
• Approximate location (region inferred from your IP address, etc.)
• Device information (OS type/version, device model)
• Ad-related usage information, such as ad impressions and clicks

We do not use advertising identifiers or any of this information to directly identify you as an individual. Please refer to Google's Privacy Policy for details on how this information is handled.

3-3. Directly Identifying Information

We do not obtain information that directly identifies you, such as your name, email address, or phone number. To the extent we collect and use the information described in 3-1 and 3-2, we do not use it to directly identify you as an individual.

4. Purpose of Use

The information described above is used solely for the following purposes:

• Identifying and investigating the cause of app crashes and errors
• Delivering ads and measuring ad performance
• Improving the quality of the App

We do not use the collected information beyond these purposes.

5. Third-Party Services

The App uses the following third-party services:

• Firebase Crashlytics (provided by Google) — collection of crash and error information
• Google AdMob (provided by Google) — ad delivery

Please also refer to Google's Privacy Policy for information on how these services handle data:
Google's Privacy Policy

6. Cross-Border Processing by Third-Party Services

Firebase Crashlytics and Google AdMob, referenced above, are both services provided by Google, based in the United States. Information collected may therefore be processed and stored on servers operated by Google, including servers located outside Japan. Google handles this information in accordance with its own Privacy Policy and applicable safeguards.

7. Security Measures

Your normal gameplay data is stored only on your device and is never transmitted externally. Information sent in connection with a crash, error, or ad delivery is transmitted and stored under the security measures Google applies to Firebase Crashlytics and Google AdMob respectively, including encrypted (HTTPS) transmission. We take care not to use the information we receive for any purpose other than those described above.

8. Data Retention and Deletion

Crash and error information, as well as information related to ad delivery, is retained in the Firebase Crashlytics and Google AdMob consoles respectively, in accordance with Google's data retention policies. For details, please refer to Firebase's privacy and security information:
Firebase's Privacy and Security information

Your normal gameplay data (board state, progress, etc.) is stored only on your device and is deleted when you uninstall the App.

9. Children's Privacy

The App is not directed at any specific age group, but we do not intentionally collect information that identifies any individual user, including children, such as their name or contact details. If a parent or guardian has concerns about how the App handles information, please contact us using the details below.

10. Requests Regarding Disclosure

If you wish to request disclosure, correction, or suspension of use of information we hold, please contact us using the details below. We will review your request and respond appropriately in accordance with applicable law. For data managed by Google, please use the methods Google provides to check your information.

11. Changes to This Policy

This policy may be revised in response to changes in applicable law or the addition of new features to the App. Any changes take effect once posted on this page. For significant changes, we will make reasonable efforts to notify users, such as through an in-app notice.

12. Contact / Complaints

If you have any questions or complaints regarding this policy, please contact us at:

shibainu.moe0324@gmail.com

We are committed to respecting our users' privacy and handling only the minimum information necessary.