Who is Kasuto?
That's probably a question that quite some Zelda fans have asked over the years. All but one of the town names from Zelda II - The Adventure of Link were later used for characters in Ocarina of Time, mostly the sages. There are the towns Rauru, Ruto, Saria, Mido, Nabooru and Darunia and we all remember the corresponding characters from the Nintendo 64 game. However, the final town with the name of "Kasuto" never saw a character with the same name.
And I just now had an epiphany, why that is. "Kasuto" is what the English translation gave us, but it's probably not what was originally intended as the name of the town by the Japanese development team. The name of the towns are written in Katakana, which is often used to transcribe English words. So, here we have:
カスト = Ka-Su-To
Both the U and the O can be silent to form the English word "Cast" and "Ka-Su-To" is actually a possible conversion of "Cast" to Katakana. And "Cast" might just be what the name of the town is, which makes thematically sense, because it's in the hidden town of Kasuto, where you find the "Spell" Spell that you only cast once in the game in the same town to find the Magical Key. You even find the last Magic Container in this town. Also, it's Old Kasuto, where you get the Thunder Spell, which you have to cast on the final boss. While every town gives you a new spell, it's really Kasuto where whole magic spell casting peaks. Which is why this town actually might go by the name "Cast".
This might not be very original, but it's not like all the towns in the Zelda series have highly original names, e.g. "Skyloft" or "Castle Town". Even "Kakariko" comes from "Cocorico", the sound of a crowing rooster in French (or it's just the clucking sound of Cuccos in Japanese). So, a town about Magic Spells being named "Cast" isn't far-fetched. This would also explain, why there never has been a character with the name "Kasuto". And if there ever will be one, he or she is probably a wizard / a spell caster.