What WaniKani leeches are and how to break them
The review asks for the meaning of 持つ. You have seen this card dozens of times, so you type "to wait", and the screen shakes red. To wait is 待つ; this one is to hold. The item slides back toward Apprentice, comes around four hours later, and you get it right while the sting is fresh. It climbs for two weeks. Then a Guru review serves it cold, minutes after 待つ appeared in the same session, and you swap them again.
待 and 持 share their entire right half; the only difference is the left radical, step on wait and hand on hold. Your memory is not failing at random. It was never given a reason to tell them apart.
The forum has called items like this leeches since 2017: anything that just will not stick.
The formula
A leech is not an official WaniKani concept, and the strict answer is that any item bouncing between Guru and Apprentice for a prolonged time qualifies. But the userscripts that hunt them settled on one score years ago. An item is a leech when it crosses 1:
Incorrect is the item's lifetime wrong-answer count from WaniKani's review statistics; streak is its current run of correct answers, floored at 0.5 so a fresh miss does not divide by zero. The SRS stage never enters it. The 1.5 exponent makes the score forgiving while a streak holds and harsh the moment it breaks: four lifetime misses on a current three-streak score 4 / 5.2 = 0.77, under the line. Miss it a fifth time and the streak zeroes, the floor kicks in, and the score jumps to about 14.
The threshold is where taste comes in. At 1.0 a single miss can flag an item; 1.01 excludes the one-miss cases; 2.0 demands at least two wrong answers before anything earns the name. Some tools also drop Enlightened and Burned items outright, on the reasoning that an item you drove that far is not troublesome enough to count. There is a no-math version too, and it is not a bad one: it is a leech if you dread seeing it come up.
The score originated in a 2017 dashboard script and now lives in WaniKani Item Inspector, which carries a dedicated Leeches table.
WaniKani only remembers yesterday's mistakes
Stock WaniKani does track failures. The Recent Mistakes widget and the matching Extra Study mode list every item you missed in the last 24 hours. What they lack is memory. A slow-cycling leech gets missed, sits in Recent Mistakes for a day, then vanishes until its next review weeks later. The items that have been failing since March are exactly the ones a 24-hour window cannot see, and nothing native looks further back.
Longer memory is script territory: Item Inspector to browse, Self-Study Quiz to drill any list you hand it, or the Shin WaniKani Leech Trainer, which takes ten at a time and retires each after three correct answers. If you would rather not install anything, Wanilog's leech list ranks your items by the same score and shows whether meaning or reading is doing the damage.
By SRS stage and lifetime accuracy, leeches pile up in a narrow band.
If none of this feels urgent yet, there may be a reason: leeches start to bite somewhere around level 25-30. Before that the SRS absorbs them quietly.
The fix follows the diagnosis
There are four failure modes behind almost every leech: similar-looking items, unusual readings, rendaku, and mnemonics that never took. Your wrong answers tell you which one you are in. Consistently the same near-twin means a confusion pair. A plausible-but-wrong reading means the reading never consolidated. A different guess every time means the mnemonic is not doing its job.
A confusion pair breaks when the contrast becomes conscious. Put 待 and 持 side by side and say out loud what differs: step radical on wait, hand radical on hold, and you hold things with a hand. Most pair-leeches die the moment the difference is articulated. The same treatment works on 人 and 入, or the three-way pileup of 大, 太 and 犬. WaniKani lists some visually similar kanji on its item pages, but the list has gaps, so the pairing is usually yours to spot in your own review history.
When there is no twin and the item simply slides off, suspect the mnemonic. WaniKani writes one story for every learner and some will not fit your head. The Meaning Note and Reading Note fields exist for your own replacement, which then appears on every future review of that item. It does not need to be respectable; an unprintable pun will outlast a polite story someone else wrote. User Synonyms are the third native lever, and the right one when the leech is really a wording dispute rather than a memory problem.
The rest is repetition outside the SRS. A cold drill serves the same item several times in a few minutes with nothing else competing, and that often does what months of correctly-spaced reviews could not. When a leech survives even that, take it to real Japanese: example sentences on jisho.org, an NHK headline, a manga panel. An item met once in the wild tends to stop being an item.
The case for leaving one alone
The forum will not back you up here. Its position is that leeches do not fix themselves, and the evidence is on its side: one thread on the subject documents three confusable words that sat unburned through eight months of passive waiting.
We dissent on one narrow case, which is triage. WaniKani teaches some vocabulary you may never meet in print. If a rare word is bouncing between Guru and Apprentice forever and you cannot picture ever needing it, letting the SRS grind it out costs you very little actual Japanese, and drilling it anyway is time taken from words that matter.
What you cannot do is make WaniKani skip it. The knowledge base is blunt: "No, there is no way to skip a question on WaniKani." A suspend-item feature request is still open. Until it lands, the users who insist route around the gap with userscripts that advance or hide items by hand, which breaks the SRS contract to protect the habit around it. We do not officially recommend it.