Naruto:
A quieter naruto that learned to keep to himself.
He bunks classes on the first week of the academy because of the teachers and students ostracism.
He wanders around the village and overhears about summoning animal companions. Getting intrigued and being desperate.
He learns the handseals and attempts the jutsu. From sneaking into the library.
Because of not having a contract first he gets reverse summoned to a forest clearing.
He finds himself surrounded by giant bears.
Naruto Impresses the bear clan and becomes the bear summoner. Like jiraya he gets trained by the bear summons and becomes just like a bear.
Imposing, strong, unyielding.
One that takes care of his problems with his fists and wrath.
...If someone wants to write something similar just research on bears first.