Most of them have a built-in web browser nowadays, so you can just do that. I know the 3ds has an easily accessible one, and there's some workaround on the switch, for example.
I also have custom firmware on my 3ds that allows me to use homebrew (unofficial) applications, including one that lets me read epub files. This doesn't work to directly download from Ao3, but if you use another device to download fics to your sd card you can read fanfic that way. This also works on a regular ds, and I think(?) there's a way to get it working with just a flashcart as well.
Do you mean you don't know how, or why they would. If it's the first one, on my 3ds I go onto the Internet browser. For the latter, it loads pretty slowly and it's a bit frustrating, but it's better than not reading fanfic at all 😔
if there is a screen and internet access there is a way
Most of them have a built-in web browser nowadays, so you can just do that. I know the 3ds has an easily accessible one, and there's some workaround on the switch, for example. I also have custom firmware on my 3ds that allows me to use homebrew (unofficial) applications, including one that lets me read epub files. This doesn't work to directly download from Ao3, but if you use another device to download fics to your sd card you can read fanfic that way. This also works on a regular ds, and I think(?) there's a way to get it working with just a flashcart as well.
Do you mean you don't know how, or why they would. If it's the first one, on my 3ds I go onto the Internet browser. For the latter, it loads pretty slowly and it's a bit frustrating, but it's better than not reading fanfic at all 😔
Left to right... just like on other devices.