People had to ride their bamboo plows long ago to enroll in things. There were no cars yet, so they would hitch a cow to their bamboo plow, and dig their way to the government office or school to enroll.
If you enroll in something new people will find you very sexy (せき). This was true long ago too. There's nothing sexier than trying to improve yourself.
Currently there are no similar looking kanji which exist in the WaniKani learning system