"Dive" = "fly into"? The words `` and `` are both read as ``, the former meaning "to fly" and the latter meaning "to jump" (generally; don't know if they are interchangeable at all). The compound-verb suffix `` means that the action "goes in (to)", "enters", etc. So the word `` means "to jump/dive into", both literally and figuratively ("jump into (doing) a mountain of homework", "butt in to someone's business", etc.). However, `` is written with the "to fly" version of the kanji: ``. Why is this? When `` means jump and `` means "into", why wasn't **``** chosen for ``? This doesn't make sense to me at all.

`` is the general term that covers all the uses of homophonous kanjis such as `` and ``. `` is a specific one, entailing some mid-air movement (such as pedaling your legs, etc.). As usual with homophonous kanjis, the specific one can be replaced by the general one, but not the other way around. In the literal sense "to dive in to e.g. a swimming pool", you can use `` as well as ``. For the metaphoric sense "jump into homework/business", `` is probably too specific because those senses do not accompany movement in the air, and you have to use the general ``.