I was looking through Kumon’s wikipedia page (it’s a program based in Japan that teaches various subjects). I found that it was founded by this guy called “Toru Kumon” but when I looked at the kanji that made up his name, it made no sense to me:
公文 公, Kumon Tōru
Why is the second 公 pronounced like that? I scoured through Wiktionary and Jisho but they never mention this pronunciation. 公 being pronounced as く doesn’t even pop up in WaniKani!
Well, with given names, people can basically do whatever they want.
Here’s a name choosing site in Japanese with various ways of potentially writing とおる listed, and not all of them have necessarily actually been used before.
Many kanji have standard name readings (nanori readings) that can be predicted. There’s a space for those on WaniKani, but they’re often not (or never?) listed. Jisho lists them toward the bottom of the kanji entry page. But there’s no rule that anyone has to use them, so you can get total curveballs occasionally.
And that’s not to say names are easy to predict if they use nanori. But Japanese people are constantly being exposed to tons of names they have to remember, and they do get pretty good at it. Sometimes it is indeed impossible though.
There are plenty of easy to read last names and first names, or at least common names with common kanji, but there are going to be some outliers with unexpected pronunciations.