The mnemonic for the kun’yomi reading of fish is very counter-intuitive. I typed in さかぬ because the mnemonic said it was soccer nu and that’s how I remembered it, only to get it wrong because it’s na and not nu. While I was a bit distracted and only glanced over the kana, I did catch the difference that it said na instead of nu. But then I later forgot what the real kana was, and since I knew the mnemonic I was given said to use nu, I did that. I feel it’s very misleading and it should at least mention that you use na there instead of nu. There’s been a few other times I encountered this type of thing but this one was the first one to really peeve me because it’s not even close to the actual reading and doesn’t indicate that anywhere.
The pronunciation of the word “nun” is pretty close to the sound of the Japanese なん, perhaps depending on your specific dialect of English, so as an auditory mnemonic, it’d work fairly well. Try to focus on the sound of it rather than the spelling of it. Maybe even say it aloud.
As far as I’m aware, nun is pronounced the same as none.
Which is also a pretty good match for なん. 
How I would remember it:
One fish to another: “Wanna play soccer?” The other fish: “Soccer, nah”.
At least for me (southern UK English) it’s a pretty terrible match. なん is much closer to the vowel in ban, man, plan, than it is to the vowel in none, bun, done, gun… (Plus the former set have the advantage for memory that the romaji uses the same letter.)
Well, I mean, “man” is マン in Japanese (as in サラリーマン), and “bun” (the hairstyle) is バン, so…
But in all seriousness, for me, なん is definitely closer to the second group than the first. I’m… not really at all sure how I’d represent the way I pronounce the first group in hiragana.
What would someone from England know about English, anyway? 
Wait, you don’t have the “arr, me hearties” West Country pirate accent, do you?
A man, a plan, a canal, Panama.
This happened a lot for me. The most aggregious one was “gin” (specificlly referring to the alcoholic beverage) used for ぎん。The number of times I typed じん made my blood boil. Strong reasons for using your own memory aids.
I don’t agree. It’s awful. Non, the negative prefix, is an exact match. None/nun is completely different. I’m not sure how you’re pronouncing it to produce an ‘a’ sound but… it’s not right. Plus my main gripe is with the mnemonic telling me to use the romanji ‘nu’ when the correct romanji is ‘na’.
The improvement that matches other WK mnemonics would be “soccer naan”.
On the other hand, getting mad at WK is useful emotional energy that you should absolutely put into getting the card right to spite them for using a bad mnemonic, so don’t let me rain on your parade 
Yet you are ok with soccer not being so.
Perhaps highlight is visually misleading, not really the meaning of the sentence.
also rōmaji doesn’t have an n.
Yeah it’s not soccer. It’s being told to use nu when the answer is na. The pronunciation of nun and whether or not that’s close enough to ‘na’ isn’t really the problem either. It’s ‘nu’ being highlighted as a way to remember the reading when nu corresponds to ぬ and repeating it for an answer is incorrect.
For me the bun/gun/fun vowel is the one which doesn’t have a close Japanese vowel equivalent.
The Dictionary of Intermediate Japanese Grammar appendix 1 on katakana transcription says that English “cat” and “cut” vowels both get mapped to Japanese ア, which I guess explains バン, though it surprised me a bit.
After having crawled through thousands of Japanese loanwords, Nun ↔ ナン is already more of a direct phonetic mapping that 80% of actual Japanese loanwords. There are some that don’t even map phonetically, but literally, or worse, partially both.
To get an idea of how off the phonetic mapping can be, not only do the the Japanese loanwords for Thursday and Sunday alliterate, they begin with the same character (サーズデー / サンデー).
the point with @polv’s reply, just in case you missed it, is that the “so” in soccer is somehow not confusing to you: you haven’t typed そかな about it.
I’m okay with it because soccer starts with ‘sa’, and ends with ‘ka’, and ‘saka’ is the correct beginning. But nun starts with and highlights ‘nu’, which is the incorrect ending.
As I’ve said, it’s not about the pronunciation. It’s about being given the wrong romanji. It doesn’t say to enter ‘so’ for soccer, but it does say to enter ‘nu’ for nun which is incorrect.
for me ぬ is so much more like “knew” or “noodle” than “nun” that i wouldn’t get confused, but i also knew さかな as fish long before i knew the kanji so i’ll just shut up now
But you’re level 56. I’m level 8. I don’t know the readings for that many kanji yet. I have a vast knowledge of roughly a thousand kanji meanings since I started WaniKani after three weeks with Heisig’s RTK, but for readings all I have is WaniKani because I don’t like the idea of studying the two other RTK books and wanted to try a learning method that’s more modern than reading another textbook. It might sound normal to you, but to me when I’m told to type ‘soccer nu’ I type さかぬ.
It tells you to type the characters in the parentheses, not the mnemonic itself. If you were actually typing what you say you type, Wanikani would shake at you because you’d get a garble of kana and alphabetic characters as neither Wanikani’s IME nor any other IME can resolve the r at the end of soccer and you just end up with そっせrぬ. The issue is that you’re mixing the characters you’re actually supposed to type in the parentheses and the literal alphabetic characters in the mnemonic.
ahhhhh, i see. you might consider getting some other japanese input beyond just kanji and the pretty useful but truly quite random collection of WK vocabulary. “fish”, for example, is a pretty common word, but you might find yourself learning other words ahead of schedule, making dealing with WK’s quirks more manageable. for a personal example, I was delighted to learn the kanji for 暫く a couple of levels ago after encountering it a bunch (usually in kana) in my reading of fiction. also the kanji for なるほど had me shouting that word (which is very common in anime and is more or less “i see”) at the screen