As someone who actually did learn Japanese through watching anime, it took me about 3 years. I started watching anime regularly in 2018 and when I was watching Hori-san to Miyamura-kun in 2021, the last two episodes had not been subtitled, so I watched them raw and mostly understood it.

A lot of people will say that it’s impossible to learn just via watching anime, but have not actually tried it. Yes, if you have subtitles on, it’s easy to let yourself totally ignore the Japanese. But it’s not impossible, and if you are focused, you can still learn even with subs turned on.

Later on, I started taking classes in Japanese at college and started learning a lot more. But just knowledge from watching anime was enough to pass an oral placement test and skip the first 2 semesters. If you are serious about learning Japanese, I recommend taking classes or studying it seriously online. There’s also better input resources than anime such as streamers or even conversation analysis audio for linguistics research.

But I am convinced that anime is still a very good tool because many people like anime and are already very motivated to watch it. This is a very big strength because the biggest obstacle to learning language is giving up. This, combined with Japanese’s very very simple grammar and verb conjugations actually makes it a very easy language to learn, imo.