Hitsugaya's early life was spent in Junrinan, District 1 of Rukongai. There he lived with his Grandmother and for a short period of time with Momo Hinamori, who he considers a very close friend.
As a child, Hitsugaya had an icy demeanor that estranged himself from others, with the exception of his grandmother and Hinamori. Throughout his childhood, he was always aware of what seemed to be an icy presence within himself and had continuous dreams about a plain of ice. He claims or believes he died on that plain. Five years after Hinamori's departure, Hitsugaya encountered Soul Reaper Rangiku Matsumoto, when she stood up to a merchant who left his change on the counter, rather than handing it to him. The two got into an argument, and Rangiku noticed Hitsugaya’s enormous latent spiritual power.
That night, Hitsugaya dreamt again of the icy plain and finally met Hyorinmaru for the first time, though he could not hear the spirit’s name. He woke up to find Rangiku admonishing him for not being able to control his power, which had been freezing his grandmother. She told him that power like his needed to be controlled, and had to convince him to become a Soul Reaper. With Hitsugaya's natural talent, he entered the Soul Reaper academy in spite of his age and became known as a prodigy/child genius, quickly ascending to Captain of the 10th Division, ironically making him Matsumoto's superior.
ōshirō Hitsugaya is very young by Soul Society standards. Born in Rukongai, he became the youngest ever to reach Captain rank (Taicho - Japanese for 'Captain'). Ichigo Kurosaki's school. He hates anything that he deems childish and hates being described as something close to a child, evident in a filler episode when he meets Ichigo's sister, Karin, who pats him over the head further angering him. Thus, he is called a "boy genius" or a "child prodigy" by many. Hitsugaya is generally mature and serious, in contrast to his free-spirited lieutenant, Rangiku Matsumoto, although he can sometimes be short-tempered and irritable. Despite their personality differences, he and Matsumoto seem to be very close. Hitsugaya is shown to also be easily irked by others goofing off or drawing unneeded attention to themselves, as shown when he led a team of Soul Reapers into
Hitsugaya's intuition is extremely sharp, and he is the first person to correctly suspect Gin Ichimaru of foul play, though he understandably did not suspect Sōsuke Aizen of the same. He is very protective of Hinamori Momo, due to the fact that they grew up together, promising to kill those who harm her. A running gag is Hitsugaya getting annoyed when anyone refers to him by anything other than his title, "Captain Hitsugaya".