Episode 356's title is 巨人 (normally pronounced きょじん, "KYOJIN"), which means "giants". Miura added the furigana ヨトゥン to indicate that it should be pronounced "YOTUN". It it a reference to Norse mythology, which features a type of beings called Jötunn (plural: Jötnar). As was often the case, while Miura applies a mythological name to give some color to Berserk's world, there's no clear relation beyond that.