Angle
When you're in prison, your only task is to count every angle in your cell. You count the angles of the walls and ceiling over and over again to pass the time. How many angles could there be in a room with four walls? Picture it and try to count those angles now.
An update is needed before you can continue but you have more than one WaniKani tab open.
Finish up what ever you are doing on the other tab(s), then close them to continue.
The update will complete automatically once the other tab(s) are closed.