Service information

Terms of service

Effective date: 25 October 2026

These terms are an agreement between you and lapis, an individual developer who makes Fusen ("we", "us"). They apply to the Fusen app for Android, its desktop companion app, the Fusen account service and Fusen AI (together, "Fusen"), including buying credits and monthly plans. By using Fusen you agree to them. If you do not agree, do not use Fusen.

1. What Fusen is

Fusen is a Japanese dictionary and vocabulary notebook for reading. The dictionary and the notebook work on your device without an account. Fusen AI, which translates passages, explains words and reads text from images, needs a free Fusen account and uses credits.

How we handle your information is explained in our privacy policy.

2. Who can use Fusen

You must be at least 13 years old to create a Fusen account. If you are under 18, or a minor where you live, you need a parent's or guardian's permission to use Fusen, and their consent before you buy anything.

3. Your account

• An account is for one person. Keep your sign-in secure and do not share it.
• You are responsible for what is done with your account. Tell us at once if you think someone else is using it.
• You can delete your account at any time in the app (Settings → Account and sync → Delete account) or as described on our account deletion page. What happens to credits and plans you paid for is described in section 9.

4. Acceptable use

When you use Fusen, do not:

• create accounts or use other tricks to get more free credits than one person's allowance, or otherwise get around credit limits, rate limits or other restrictions;
• access our server other than through the Fusen apps, use it automatically or in bulk (for example to scrape or to resell its answers), or try to interfere with it, overload it or break its security;
• send content that is unlawful, that infringes someone else's rights, or that you have no right to send;
• use Fusen AI to produce content that is unlawful or harmful, or in ways that break the usage policies of the AI providers listed in our privacy policy, which apply to everything Fusen AI sends them;
• copy, sell or redistribute the Fusen apps or our service, except as the law allows.

5. Your content

• Your notebook, and the text and images you send to Fusen AI, remain yours. You give us permission to process them only to provide Fusen to you, as our privacy policy describes.
• Make sure you are allowed to use the text and images you send. Using Fusen to help you read a book or manga you have is fine; Fusen's answers are for your own reading and study, not for publishing or sharing a translation of someone else's work.
• If you rate an answer or report a problem, you allow us to use what you send to improve Fusen.

6. AI answers

Fusen AI's translations, explanations and text read from images are produced automatically and can be wrong, incomplete or misleading. Check anything important, and do not rely on Fusen AI for legal, medical, financial or other professional advice. You are responsible for how you use its answers.

7. Credits

• Fusen AI uses credits. How many credits a request uses depends on the feature, the model and the length of the text; the app shows the current amounts. We may change them, the models Fusen AI uses and which features are offered. Changes apply to requests made after them, not to credits you already have.
• Free credits: each account gets a free allowance each month, as the app shows. We may change the allowance. Unused free credits do not carry over to the next month.
• Plan credits come with a monthly plan and paid credits with a credit pack (section 8).
• A request uses free credits first, then plan credits, then paid credits.
• Credits of any kind are a right to use Fusen AI. They have no cash value, cannot be exchanged for money (except by a refund under our refund policy or section 10) and cannot be transferred to another account.

8. Buying credit packs and monthly plans

• Prices are shown in the app before you buy and include any tax. Stripe's checkout page may show and charge the price in your local currency; the amount on that page is what you pay. Your card issuer may add its own fees.
• Payment is processed by Stripe, our payment provider, on its checkout page. Your purchase is complete when the payment succeeds. Credits are added to your account as soon as the payment is confirmed, usually at once; a slower payment method can take longer.
• Credit packs are one-time purchases. Their paid credits do not expire while your account exists.
• Monthly plans renew automatically every month, on the day of the month you subscribed, at the plan's price, until you cancel. Each paid month gives you the plan's monthly credits for that month, replacing any plan credits left from the month before: unused plan credits do not carry over. If a renewal payment fails, Stripe tries again for a while and your plan credits stay usable until shortly after the end of the month paid for; if the payment still fails, the plan ends. An account can have one plan at a time.
• Cancelling or changing a plan: you can cancel or change your plan at any time in the app (Manage plan, which opens Stripe's page). A cancelled plan stays active, with its credits, until the end of the month you paid for, and nothing more is charged. A change to another plan takes effect at the next renewal. Except as our refund policy says, we do not refund part of a month.
• Price changes: we may change prices. A new price for a monthly plan applies to you only from a renewal at least 30 days after we tell you about it in the app or by email, so that you can cancel before.
• Refunds: our refund policy explains when you can get your money back, including a refund within 14 days of a purchase whose credits you have not used. It does not limit any right the law gives you.

9. Paid credits and plans when an account ends

• If you delete your account, its unused paid and plan credits are lost and its plan ends at once, without a refund. If a recent purchase can still be refunded under our refund policy, ask for the refund before you delete the account.
• If we close your account because you broke these terms, its unused paid and plan credits are lost and its plan ends, unless the law requires otherwise.

10. Other services and dictionary data

Some features use services from other companies, such as Google sign-in and Google Drive, or a translation engine you choose with your own key. Their own terms apply to your use of them, and we are not responsible for them. Fusen's dictionary data comes from third parties under their own licences, for example JMdict from the Electronic Dictionary Research and Development Group under the Creative Commons Attribution-ShareAlike 4.0 licence. The app lists these sources and licences.

11. Changes to Fusen, suspension and ending

• We may change, add or remove features, and may need to interrupt Fusen for maintenance or because of problems outside our control.
• We may suspend or close an account that breaks these terms, or whose use puts Fusen or other people at risk. Where we reasonably can, we will tell you first and give you the chance to explain.
• We may stop offering Fusen or Fusen AI. If we do, we will announce it in the app or on this website at least 30 days in advance, stop charging monthly plans, and refund the paid credits from credit packs that are left unused when Fusen AI stops, in proportion to the price you paid for them. Your notebook stays on your device and in your own Google Drive, and you can export it.

12. Disclaimer and limitation of liability

We work to keep Fusen useful and available, but provide it as it is and as available, without promising that it will be error-free, uninterrupted or suited to a particular purpose.

If we cause you damage intentionally or through gross negligence, we are liable under the law without limit. If we cause you damage through ordinary negligence, our liability is limited to direct and ordinary damage actually incurred, up to the greater of the amount you paid us in the 12 months before the damage occurred and US$100.

Nothing in these terms limits any liability, or excludes any right you have, that the law does not allow to be limited or excluded, including under the consumer law of the country where you live.

13. Governing law and disputes

These terms are governed by the laws of the Hong Kong Special Administrative Region. If a dispute cannot be settled by talking it through, the courts of Hong Kong have jurisdiction. If you are a consumer, you keep the protection of the mandatory laws of the country where you live, and you may also bring a case in its courts where that law allows.

14. Changes to these terms

We may update these terms, for example when Fusen changes or the law requires it. We will post the new terms here with a new effective date and, for changes that matter to you, tell you in the app before they apply. If you keep using Fusen after that, the new terms apply; if you do not agree, you can stop using Fusen, cancel your plan and delete your account. A change does not take away credits you already paid for.

15. General

• If part of these terms is found invalid, the rest stays in force.
• These terms are written in English. If we provide a translation, it is for convenience, and the English version governs.

16. Contact

support@fusen.ink

See also our privacy policy, refund policy and support page.