I can see the difficulty of integrating with Anki if you're trying to implement a sophisticated system for tracking a user's progress, however I would definitely want some way of studying vocabulary with spaced-repetition flashcards I could have on my phone for something like this, Anki or otherwise. I've personally found traditional flashcards and (even more so) writing words with pen on paper to be the most effective ways of absorbing vocabulary. I've found that I don't ultimately absorb vocab as well using other self-quiz methods like multiple-choice / fill-in-the-blank / matching / etc. in Duolingo and similar apps (though I've had the false impression of learning from these methods). Just my personal experience.

It seems we're on the same page regarding specific word-meanings, comprehensive linguistic information provided along with a word, and using good dictionaries.

I would suggest including at least the option of viewing the full conjugation / declension / etc. associated with a word, and not just that used in the context of the text. I don't know any Japanese (though I recognize the example character you provided from the little Chinese I've studied), but something like this full conjugation of that verb is roughly what I'd want to see for any conjugated/declined language: http://www.japaneseverbconjugator.com/VerbDetails.asp?txtVer....

I understand parsing and matching up parallel texts is difficult, but I thought NLP would help with that, and if the software fails at matching up individual words, you could default to matching up clauses or sentences, which the user could study (with flashcards or something similar) alongside the individual words taken from the dictionary.

I took a look at the app, but I see the currently-available demo is only English-Japanese, and I'm also consistently getting "API Error: Request failed with status code 412" in multiple browsers.

Exactly what parts of the app are you looking for someone else to work on?