Japanese Language

Listen to more comprehensible stuff is one thing. Then you can use subtitles, either Japanese or English. I leave that up to your willingness to SUFFER, but as you probably know up to a point the more you suffer the more you learn so yeah. And whatever you do you have to keep at it; no matter your studying method you need time to get results. Also this is unrelated but 研エンの仲 is a great title and I need to know what the エン stands for.

Watch videos with Japanese captions. Expect this to be a lot more like homework than enjoying a video. Be ready to pause the video and look up words regularly. Keep a notebook of words you've been learning.

That helped me a lot.

Another thing that helped me a lot was reading / listening to Breaking into Japanese Literature. This is not niche like you are looking for, but it really helps with listening comprehension.

I have this too, I think it is mostly just our vocab being too small still. If you know all the words but not all the grammer, you can guess/infer pretty well and by doing so learn by listening. But if you don't know the words (even if you know the grammer) they might as well be saying "The blabla is blabla and blabla was blablaed". I try to learn from a more structured source (book, app, website, etc) and then when I listen to things I can pick up more words that I then recognize. Which are then reinforced into me. Personally I make sure to practice Japanese before I watch an anime episode to get this process going, or at least make sure I don't skip out on the more boring work. I do feel I improve slowly over time. Don't think there is a special way to go or any shortcuts, you just need to keep studying as well as consume content.

As you've already discovered, the answer is to instead focus your listening on simpler material like Nihongo con Teppei. I'm an acolyte of Krashen's i+1 input hypothesis for second language learning: we progress in language learning when we're exposed to input that is slightly ahead of our current level. I do think intermediate level can be a real struggle because there is tons of beginner-level material out there and (of course) endless native material, but the stuff in the middle is much harder to find. It really does have to be modified/simplified in some way from native level to be effective. Even native materials for kids doesn't always work out because they learn the language differently than we do.

Also, while I read more than I listen personally, within groups of material that we know is an appropriate level it's a good idea to push right past the stuff that's totally incomprehensible--it happens--and concentrate on the i+1 content. Do a quantity over quality approach when possible. I find this naturally easier to do when listening; it's too easy to stop constantly and go on a text parsing or copy/paste spree to dissect sentences when reading.