Okay kiddo, so you know how Japanese has three different writing systems? There's hiragana, katakana, and kanji. But did you know that there are some letters that don't fit into any of those three? That's where yotsugana comes in!
Yotsugana are four special letters that are sometimes used in traditional Japanese writing. They're called "yo-tsu-ga-na" because "yotsu" means "four" in Japanese. The letters are "wi", "we", "wo", and "vu".
Now, these letters aren't used as much in modern Japanese writing anymore, but they're still important to know about because they were used a lot in the past, and they're still used in certain contexts, like for people's names and in historical documents.
So, that's the basics of yotsugana - four special letters that don't fit into the usual hiragana, katakana, or kanji systems. They're not used as much these days, but they're still important to know about if you want to understand traditional Japanese writing.