Are there a ton of kanji that have meaning that are vastly different from each other? I usually only read the main meaning that pops up real quickly as I study new items. But stuff like the kanji for sky also meaning empty (to make karate empty hand) is interesting to know. I’m just curious if it’s super common?
It is quite common. Sometimes I notice these meaning when I learn the kanji and they stick. Something I only worry about the extra meanings when learning the associated vocabulary. It might help to look ahead when learning the kanji at the vocab that Wanikani will teach for that kanji, later on. That’s not totally representative of the words you’ll encounter in the wild, but it could give an indication of where the extra meanings come up a lot.
Sometimes it’s not so much that the meanings are really different, it’s just that they’re very abstract and cover a lot of ground. 振 is a decent example of that, it’s used in many different words that often translate very differently in English but they generally share a common sense of “not going straight” or “wobbling”.
頂 is another one of those, it means “top of head”, “summit” and “receive” but all these meanings are in fact related, the idea being that if you receive humbly (頂く) then you cherish the thing being handed to you by placing it above yourself.
You also have cases where two kanji merged due to simplifications. 干 is a good example: it means either “dry” or “interfere” which seem rather unrelated, but that’s because the “dry” kanji was originally 旱 and they just decided to drop the 日 and use 干 for both.
I frankly wouldn’t worry too much about this when studying the kanji in isolation, it’ll come with the vocab.