When learning hiragana and katakana, we’re quick to notice that some are missing. wu, we, yi… wi (ゐゑ) and we (ヰヱ) are in Unicode and in most fonts, as they were used all the way up until the 1950’s and show up sometimes even now (in places like usernames). Type them in the romaji-style input by writing “wyi” and “wye”.
There is no yi, ye or wu. Historically speaking, the Y sound is really just a short I with a bit more forceful breath, so yi would really be ii. E is the sound created in-between I and A, so it would have historically been iia for the same reason. The Japanese W is actually the same exact sound as its U, it’s just that U uses the voice and W is simply a puff of breath, so saying the two fast and close together is just too difficult (it’d be like saying “sz, td, pb”). Our English W is slightly different from our U, which is why we can say “woo” and Japanese can’t.