Getting connected to kaeru:world requires custom firmware, but don't fret - it's all explained here.
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About custom firmware
Due to the way in which the Nintendo 3DS handles network interactions, we need to apply a patch at runtime to redirect Flipnote Studio 3D to the kaeru:world server - this is only possible with custom firmware owing to Nintendo's system security measures against unsigned code. The most popular such firmware is called Luma3DS, which is what we officially support.
Although it may seem scary to mess with your console's software, the process of installing custom firmware on a 3DS has never been easier nor safer! We recommend reading 3DS Hacks Guide to take you through the process - this guide is widely regarded by the homebrew community as the definitive guide to 3DS homebrew setup, and is written to be clear and simple. Once you've done that, pop back here to get kaeru:world setup.
Please note that it is not recommended to follow video guides when setting up custom firmware, since they are often outdated and as such may lead to problems later on, due to the ever-changing nature of the 3DS homebrew scene.
If at any point during this process you have any questions or concerns, send us a message in the #support channel in our Discord guild. Someone will usually help you quite quickly, depending on timezones.
Copy the extracted 'luma' folder to the root of your SD card (that is, copy the folder itself) - if asked to merge, choose 'yes'.
Next, we need to enable game patching in Luma3DS.
Hold the Select button whilst powering on your console to bring up the Luma3DS configuration menu, which should look like this:
Use the directional pad to highlight 'Enable game patching' as shown, and press the A button to enable it. Press the Start button to save and continue booting.
What's the 'root' of my SD card?
The term 'root' in this context means not within a directory. You should have a 'luma' folder at the root of your SD card, among others, looking something like in this image (click for full size):
Open 'Flipnote Studio™ 3D' from the Nintendo 3DS HOME Menu and scroll to the right hand page. Select 'kaeru:world' (English) or 'Nintendo DSi Library' (other languages - we are working on translating our patch's strings).
If you do not receive an error, you're all set! Enjoy Kaeru, and remember to join us on Discord! Also, please consider donating to Kaeru Team so that we can keep services like this alive and kicking even when Nintendo can't (:
If you encounter a black-screen exception error, ensure you have the latest version of Flipnote Studio™ 3D downloaded from Nintendo eShop&tm;.
To do this, open Nintendo eShop on your Nintendo 3DS console and select Menu -> Settings / Other -> Redownloadable Software -> Titles You've Downloaded and find Flipnote Studio 3D. Select it, and choose the option to update (if available) or otherwise find the 'Repair Software' option and use that.
If you encounter a message stating that the console has failed to connect, check your internet connection - can you access web pages from the Internet Browser? If so, let us know via Discord - something has probably gone wrong at our end.