Ichigo Kurosaki is the younger twin brother of Hiroshi Kurosaki by five minutes.
When Masaki Kurosaki, their mother, died Hiroshi and Ichigo where there, and later on Ichigo gets blamed for his mother's death.
Hiroshi secretly beats Ichigo up every day, and one day he can't take it anymore. He leaves Karakura town, and settles in the next town over.
The same events that happen in the manga happen the same way only it happens to Hiroshi instead of Ichigo.
Later on Urahara suggests to Renji, Rukia, Orihime, Chad, Hiroshi, Uryu, and Toshiro to find Ichigo and persuade him to help in the winter war, only thing is Hiroshi is extremely against it.
Urahara explains to the others, excluding Hiroshi, that Ichigo had left with his own secrets and could help in the war.
The group excluding Hiroshi go and search for the orange haired teen, but when they find him it definitely isn't what they expected.