Terms of Use
Last updated: 6 October 2026
These Terms govern your use of Katsu: JLPT Quiz & Kanji (“Katsu” or the “App”) on Android and iOS and its related services, provided by VIODRA STUDIOS BILISIM HIZMETLERI SANAYI VE TICARET LIMITED SIRKETI (“VIODRA STUDIOS”, “we”, “us”). Katsu was previously distributed under the name JLPT Quiz: Kanji & Vocabulary.
Contact: support@viodrastudios.com
Postal address: İcadiye Mahallesi, Cemil Meriç Sokak, Girne Apt. Blok No: 87/5, Üsküdar, 34674 İstanbul, Türkiye.
By using the App, you agree to these Terms to the extent permitted by applicable law. If you do not agree, do not use the App. Mandatory consumer rights and any rights that cannot legally be excluded remain unaffected.
Our Privacy Policy explains personal-data processing. Accepting these Terms does not provide consent to optional advertising tracking or other processing that requires a separate choice.
1. What Katsu provides
Katsu is an independent Japanese-learning application. Available features can include Kanji and vocabulary study, grammar, reading and listening practice, quizzes, favorites, study statistics, achievements, game-style practice, Kanji TV, downloadable audio and progress backup.
Katsu is not an official JLPT product and is not affiliated with, endorsed by or operated by the Japan Foundation or Japan Educational Exchanges and Services (JEES). References to JLPT levels describe study categories. App scores, achievements and completion records are not official qualifications or predictions of an examination result.
We aim to provide useful, accurate content, but translations, readings, explanations, questions and audio can contain errors or admit more than one interpretation. You can report an issue through the available reporting tools. We do not guarantee a particular language-learning outcome or examination score.
2. Permitted use
You may use the App for your own lawful learning and personal use, subject to these Terms, applicable law and the relevant store’s usage and access rules. You are responsible for the actions you authorize through your device or account.
Where applicable law requires a parent’s or legal guardian’s authorization to use the App, agree to these Terms or make a purchase, that authorization is required.
3. Accounts, guest use and separate identities
You can use available learning features without signing in with Google or Apple. Guest use may still involve an automatically created technical authentication account, as explained in the Privacy Policy.
Optional Google and Apple sign-in support account and learning-data features. Use accounts you are entitled to access and keep your provider credentials secure. Katsu does not receive your provider password.
Three different identities may be involved:
- Katsu sign-in: the profile and learning records associated with your app account.
- Cloud storage: the Google Drive or iCloud account holding a backup.
- Store purchases: the Apple or Google store account and purchase records used to establish Pro access.
These identities are not interchangeable. Signing into Katsu does not, by itself, synchronize every device, restore every backup or transfer purchases between Android and iOS. Linking a sign-in provider must not be understood as merging two people’s purchases or cloud accounts.
4. Free features, Pro and advertising
Katsu offers free features and may offer additional access through Pro, available subscriptions, a lifetime purchase or a clearly described rewarded-ad action. The current in-app offer explains the included features and any applicable limits. Feature availability may differ by platform, version or region.
The free version can contain advertising. Active Pro access suppresses the in-app advertising covered by the Pro offer. Advertisers’ products and external pages are provided by those third parties; displaying an ad does not mean we endorse them.
Rewarded ads are optional offers for the specific benefit shown in the App. A reward is granted only when the required completion is confirmed. Merely opening or closing an ad, declining a privacy permission, or encountering an unavailable ad does not establish that a reward was earned. A reward is not money, cannot be exchanged for cash and does not become a general Pro purchase unless the offer expressly says so.
Ad availability is not guaranteed. Your privacy choices may affect whether and which ads can be shown. A failed ad does not remove consumer rights relating to a separate paid purchase.
5. Purchases, subscriptions and lifetime access
Prices and payment
Purchases are processed by the relevant app store. The store’s purchase confirmation displays the applicable price, currency, billing period and other terms. Prices may vary by country, tax treatment and store. The App does not collect your full payment-card details.
Only the offer displayed and confirmed at purchase creates a purchase obligation. There is no free trial unless one is explicitly offered and described in that confirmation.
Monthly and annual subscriptions
Subscriptions provide the stated access for the purchased period and normally renew automatically until canceled under the store’s rules. An annual subscription is billed for the annual period; a displayed monthly equivalent is a comparison and does not turn it into monthly installments.
Manage or cancel renewal through the store that billed you. Cancellation generally stops a future renewal rather than immediately refunding a completed payment, subject to the store’s terms and applicable law. Access normally continues for the remaining paid period unless a refund, revocation or another store action changes the entitlement.
Deleting Katsu, signing out, disabling backups or deleting your Katsu account does not cancel a store subscription. You must manage renewal separately through Apple or Google.
Lifetime purchase
A lifetime purchase is a one-time, non-renewing purchase of the stated Pro entitlement. It does not require a recurring subscription payment for that entitlement. It does not promise that the App, every external service, or every future operating-system version will exist or remain supported forever, and it does not automatically include separate future products or purchases in another store.
We will not turn an existing lifetime entitlement into a recurring subscription merely by changing these Terms. Any change or discontinuation affecting purchased access remains subject to the offer made at purchase and mandatory consumer remedies.
Restoration and entitlement checks
Purchase verification and restoration depend on records from the relevant store and supporting services such as RevenueCat. Use the same store account that holds the purchase and the App’s Restore Purchases option where needed. An internet connection may be required to verify or refresh access.
Katsu sign-in is not required for same-store purchase restoration. The current product does not provide cross-platform Pro sharing through a Katsu account: a Google Play purchase does not automatically become an App Store purchase, or vice versa. Learning backups do not contain a transferable Pro entitlement.
Refunds, reversals, expiration or store revocation may end the corresponding entitlement. Verification problems can temporarily prevent us from confirming access; contact support if you believe a valid purchase is missing.
Refunds and purchase changes
Refunds and cancellation rights are governed by the store’s procedures and applicable law. These Terms do not impose a blanket “no refunds” rule. Contact the billing store or us for help with an incorrect or inaccessible purchase. Any price or subscription-term change must follow the applicable store notice and consent requirements.
6. Progress, backups and changes of device
Learning records are primarily stored on the device. Signing out can leave the former account’s local records on that device while starting a separate guest session. Removing app data, losing a device or using a replacement restore can affect your progress.
Optional backups use Google Drive on Android and iCloud Drive on iOS, with supported manual export/import and Google Drive import flows. A sign-in account is not, by itself, a guarantee that a backup exists. Review the backup setting and the last successful backup status before relying on a copy.
Automatic backup is not continuous real-time synchronization. It depends on app activity, provider access, available storage, network access and a successful operation. Device and cloud copies can differ. Where offered, a merge combines supported records; a replacement changes the relevant local records to the selected backup. Read the confirmation before replacing data.
Portable backup files contain private learning/profile information and can be imported without a password or the original account. Keep them secure. Do not import another person’s private backup without authorization. Exporting a file or opening a share sheet is not proof that a durable backup was saved.
Updating from an earlier Android version can migrate compatible records and verify eligible earlier purchases. Compatibility handling does not guarantee recovery of every damaged, missing or unsupported historical file. This does not limit any legal obligation we have to provide the service with reasonable care or remedy a defect.
7. Downloads, audio and connectivity
Some learning content is included with the App, while some listening packages require a download and an eligible entitlement. Downloaded content can be used as supported by the App, including offline use where available, while the applicable access conditions continue to be met.
Downloads, sign-in, purchase verification, advertising, cloud backups, reporting and remote configuration can require internet access. Your mobile or internet provider may charge for data. A download may need to be retried after interruption; keep enough device storage available.
Pronunciation can use the text-to-speech service selected on your device. Voice availability, quality and any network requirement depend on that service and its settings. Listening practice plays educational audio and is not a service for recording or assessing your microphone input.
8. Reports, feedback and support
You may submit content-error reports or contact support. Provide accurate information and include only information you are entitled to share. Do not put passwords, payment-card details or unnecessary sensitive information in a report.
You retain any rights you have in your original feedback. You give us permission to use that feedback as reasonably necessary to investigate the issue, communicate with you, correct learning material and maintain the App. This does not grant us unrestricted rights to publish your identity or private correspondence.
A submission receipt confirms receipt, not acceptance of a suggested answer or a promise to implement a change by a particular date. We may correct or decline a report after review. Support correspondence and content reports are not public discussion posts in Katsu.
9. Intellectual property and fair use
The App’s software, original learning material, artwork, audio, branding and presentation are owned by us or licensed to us, except where identified otherwise. A purchase grants access under the applicable license; it does not transfer ownership of the software or the complete content collection.
You may use the App’s intended export and sharing functions for their stated purpose. You may not otherwise redistribute or sell the App or its content collections, bulk-extract protected datasets or audio, remove rights notices, impersonate the publisher, or bypass purchase and download authorization controls. Exceptions permitted by law and the licenses of open-source or third-party components remain available.
Do not interfere with the service, submit malicious files, abuse report or download endpoints, conduct fraudulent purchases or refunds, or access another person’s private account or data without authorization.
10. Permissions and external services
Optional features can request relevant permissions or account access, such as photo selection, notifications, cloud storage or iOS tracking. Declining a permission can prevent the associated optional feature from working. It does not by itself cancel a purchase or make you agree to another form of tracking.
Google, Apple, RevenueCat, advertising providers, cloud storage, your mail application and other services have their own applicable terms. They control their services, account availability and billing or storage rules. We remain responsible for our own obligations and do not use those third-party terms to exclude rights you have against us.
11. Updates and service availability
We may release updates, correct learning content, change feature implementations and address security or compatibility issues. You may need an update or a supported operating system to continue using certain features. We do not guarantee uninterrupted availability of every online service.
If a material change would reduce a purchased service, we will provide any notice and remedy required by the purchase terms and applicable law. These Terms do not give us an unrestricted right to remove paid access without a lawful basis or applicable remedy.
12. Ending use, account deletion and restrictions
You may stop using the App at any time. Signed-in users can request account deletion through Profile → Delete account. Once successfully completed, this process removes the app account and its corresponding local learning/profile records on the device where deletion is performed; other copies and records are described in the Privacy Policy.
Manage subscriptions separately and remove any cloud or exported backups you no longer want. Deleting an app account does not delete your Apple/Google account, automatically erase all copies on other devices or guarantee removal of transaction records that must remain available.
We may take proportionate action to protect the service against material misuse, fraud, security threats or unlawful activity. Where appropriate, this can include restricting an abused online function. We will provide notice or an opportunity to resolve the problem when reasonably possible, except when immediate action is needed for security or legal reasons. Any restriction affecting a paid service remains subject to applicable consumer rights.
13. Responsibility and limitations
We provide Katsu with reasonable care and aim to correct material problems brought to our attention. Educational content and software cannot be guaranteed error-free, and study results depend on factors beyond the App.
To the extent permitted by law, we are not responsible for losses that were not reasonably foreseeable, business losses arising from use of a personal learning app, or failures caused solely by a third-party service outside our control. This does not excuse our own failure to meet an applicable legal or contractual obligation.
Nothing in these Terms excludes liability that cannot lawfully be excluded, including applicable liability for fraud, intentional misconduct, gross negligence, death or personal injury caused by negligence, or mandatory rights relating to defective digital content and services. Any statutory remedy, refund or compensation right takes precedence over a conflicting limitation here.
14. Store licenses
App-store downloads are also subject to the relevant store’s terms and usage rules. For an iOS download, Apple’s Standard End User License Agreement applies to the app license unless a different applicable license is supplied through the App Store. These Terms describe Katsu’s services and do not replace mandatory store-license provisions or reduce your statutory rights.
VIODRA STUDIOS is the provider of Katsu. Contact us for App support; store billing and refund requests may need to be handled by the relevant store.
15. Applicable law and disputes
These Terms are governed by the laws of Türkiye, except to the extent that mandatory laws of your country of residence provide protections that cannot be displaced. Nothing here prevents you from bringing a claim before a competent consumer body or court available under applicable law.
Please contact support@viodrastudios.com so we can try to resolve a problem. Contacting us first is not a waiver of a legal deadline or a requirement to give up another available remedy. These Terms do not impose mandatory private arbitration or a class-action waiver.
16. Changes to these Terms
We may update these Terms to reflect changes to the App or legal requirements. We will show the revised date and provide additional notice or obtain agreement where required for a material change. Changes do not retrospectively remove accrued consumer rights or automatically change the terms of an existing store subscription.
If a provision is unenforceable, the remaining provisions continue to apply to the extent permitted by law. For any question about these Terms, contact support@viodrastudios.com.