The pronounciation of 円 is actually en, but it's written out as "yen", it's the remnants of Japanese from about 100 years ago.

Since late-Edo until the Meiji period it was written as "をたく".

In English that'd be Wotaku.

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It was also in that time that you'd get ゑ （we) and ゐ （wi) I think. Those characters are now no longer in common use. There is a particular anime director who decided to use the obscure ヰ(katakana of ゐ) in his name, it's possible that's the kana they used ages ago - カサヰケンイチ (Kasai Ken'ichi)
Another use of o -> wo might be in the name かをる Kaworu (Kaoru). Wasn't there a character like that in Eva? Reminds me of using "ho" for "o" like in なほこ (Nahoko) for なおこ (Naoko) though I think it's a bit different.