WaniKani Keyboard Focus
This is a very limited-scope script that solves, an admittedly probably very niche issue: The annoyance of losing keyboard focus from the main input bar during lessons. I wrote this script, because I would find myself accidentally clicking off the input box, and being annoyed when typing didn't produce any characters.
I also use WaniKani Double Check (which is a must-have script), and you can also click off the input when you get a question wrong, and then open the subject info notes. This can happen rather more frequently than you might think using this script, if, for example, WaniKani will not accept a certain Meaning that you think is absolutely correct, but you want to verify it before getting it wrong, or switching to something WaniKani will accept.
This script is not intended to work with every other script out there, since it takes control of input focus. It works well with the scripts I use, but may not play nice with others. If you want to use this script, but find that it interacts poorly with another script, you can disable it by clicking the "glasses" icon.
The script does, however, respect WaniKani lesson navigation. For example, it will give proper focus when adding synonyms, user meaning hints, and when transitioning between lesson batches ("Next batch, please!").