As of chapter 31, Kukai's four older brothers are introduced. The first and oldest is Kaidou (海童, Kaidō), the second is Shuusui (秀水, Shūsui), the third is Unkai (雲海, Unkai), and the fourth is Rento (れんと, Rento). All of their names have kanji meaning either the sea, or sky, or have a relation to it, including Kuukai, but not Rento because his name has no kanji. This is possibly the reason why his Guardian Character is named Daichi, although without kanji, daichi (大地, daichi) means earth.