Here is I love my kindle despite having bad feelings about Amazon. @divinekangaroo
While I own some kindle books I mostly use my kindle with Libby for checking out and reading books from my city’s library (all the e-books for free) and for reading novel and novella length fanfic on ao3.
Here is how I get ao3 fic onto my kindle.
0. Prerequisite: Your kindle must be connected to WiFi.
1. I find a fic via my phone or computer that I want to read and note down the title and author. I do this step on my phone/computer because the browser on kindle is really bad. E-ink cannot handle scrolling down a webpage. Once title and author is noted down:
2. I go to the home page on my kindle and select the three dot menu to get to the web browser:
3. Kindle’s web browser sucks and requires your patience. Be zen. Type in www.archiveofourown.org and if you don’t include the www it will fail. Once you are in the archive, use search for the title of the fic and be patient with how horrid the browser is — reading fic is impossible in the kindle browser because the UX is shit.
When you find the fix you want, click into it. Continue to be patient.
Eventually it will load and you are almost there!
5. Tap on the download menu and select AZW3. The kindle browser will quickly tell you it has downloaded it onto home.
6. Get out of the browser (good bye good riddance you horrid dog of a browser) and go to the kindle home page. The ao3 fic is there (sitting next to library books which are also free :)
Whoo hoo!!! Fanfic the size of an extra thick novel length epic on the kindle!!!
Yay fanfic on kindle!! Read without interruptions from phone! Yayayayayay!
It is really that simple.
Other people have transferred AZW files from their computer to their kindle. I haven’t tried that. Others claim they can mail the fic to their secret Amazon kindle email account, and I have not tried that either recently (have done this in the past with mixed results). This (the above) works for me every time with no hiccups.
(See notes for further discussion)
You can in fact do the same thing on a kobo (both syncing with Libby and AO3) though you'll want to download an epub from AO3 when you get there.
On my model the browser is hiding behind beta features in the 'more' section of the menu. Kobo's browser is perhaps even glitchier than kindle's though; sometimes it can't manage the ssl handshake with cloudfare, and then you have to reset and start over, so it's definitely easier to get unlocked fics because Fewer Attempts To Access Website.
And the links all work, too! So you can jump to notes or footnotes in the fic itself, and it will open the browser from the metadata links at the beginning (if your wi-fi's on, obv, for that last one)
The caveats are the same as with kindle, it is in fact quite slow, it's MUCH easier if you already know where you're going so you really do need to plan ahead for whatever you want to read, etc but it is functional.
I don't usually do it this way, I'll go to ao3 on my computer and download an epub into calibre and then transfer to the e-reader, BUT, direct downloads are possible if you can't/don't want to do that.
Unrelated but FYI: Kobo does also have a kobo plus subscription which is similar to kindle unlimited (three tiers: just books, just audiobooks, or both) that I have heard mostly very good things about, though I haven't been reading enough lately to have set it up myself yet.
Remember that authors do not like having their fics added to Good Reads, and Kindles have a Sync to Good Reads option. If you are adding your fic to your Kindle, please turn off that sync. I have older software because I jailbroke mine, but for me it's under All Settings > Your Account > Goodreads.
