If you've put months into WaniKani, the last thing you want from a new app is to be quizzed on 一 like a stranger. Yokoso imports your WaniKani progress so known kanji stay known: reviews continue on a schedule scaled to your SRS stage, and everything you've burned or mastered is treated as exactly that.
Calls go directly from your device to WaniKani's API — there is no server of ours in between. Your token stays on that device unless you turn on sync; with sync on it travels inside your sync data, over an encrypted connection, and is stored in your private sync row, so the import keeps working on your other devices too. Items WaniKani taught you that Yokoso doesn't have content for are carried as imported items with recognition reviews — your knowledge, tracked honestly.
WaniKani is a kanji system; Yokoso is a life-in-Japan system. WaniKani won't drill you on the price the register just said, the sign on the shop door, or the pattern behind これをください — and Yokoso won't replace a 60-level kanji curriculum. Import once and each app does what it's best at, without re-teaching the other's work.
Late-level accounts used to hit a ceiling here, because the material ran out well before their kanji did. That is no longer the case. The web app now covers vocabulary and kanji from N5 through N1: 8,959 items, of which 2,056 are kanji, or about 96 percent of the jouyou set. An import at level 40 or beyond gets credited right across that range rather than only against the early bands, so a burned item counts as known wherever it lands.
What is left after the import is the part WaniKani does not do: the vocabulary around the kanji, in the registers the situation calls for. That is N3's connective words, N2's workplace and newspaper layer, and N1's formal written register and rare readings. Kanji you can already read make that vocabulary far cheaper to learn, which is exactly the sequence the import is meant to protect.
The Bunpro import is currently paused: Bunpro removed the public API it used, which is on their side and not your key. If they restore one, it resumes with nothing for you to do. The WaniKani import is unaffected and re-syncs daily.
Import your progress freeYokoso is an independent app and is not affiliated with or endorsed by WaniKani or Tofugu. The import runs in the browser, so it works from the web app the day it ships; the install guide covers putting that on your home screen and why the App Store copy runs a few weeks behind.