Hitsugaya comes from Junrinan, District 1 of Rukongai. There, he lived with an old woman (said to be his grandmother), Momo Hinamori, and possibly other people. Little else is known about his past, but it is known that he became a Shinigami shortly after Hinamori. He is also a friend of Jidanbou, the West Gate Keeper, and was the one who taught him the “city rules.”

As a child, Hitsugaya was a bit of a brat who liked to eat watermelons and poke fun at Hinamori. She would call him “Shiro-chan” (シロちゃん, “Lil’ Shiro” in the English dub) and he would counter by calling her “Bed-wetter Momo.” The two were close friends and Hitsugaya, despite being younger and much shorter than his friend, always felt that he needed to protect her. His favorite foods are watermelon and sweet nattō. He also hates hot weather.

With Hitsugaya’s natural talent, he quickly entered the Shinigami institute shortly after Hinamori, despite his age. She continued to call him “Shiro-chan” out of habit and felt she needed to protect him. Because of a promise she had made, she only began to call him “Hitsugaya-kun” after he had achieved his Zanpakutō’s initial release and was recognized as a Shinigami. Highly capable and knowledgeable, he quickly became the youngest of the Captains within the Gotei 13 (Thirteen Court Guard Squads).

(Source: Wikipedia, BleachExile)