Kirai when he still was human, and about 10 years old.
No, he didn't grow up with parents who loved him and friends he could play with. He actually was hated by everyone, and later on he also started to hate humans more than everything. (Oh, and yes, the reason why everyone hated him is because of his eyes so that's why he hides them. ^_^)
And there you go, the answer why he's name is Kirai 8D Means hate in japanese. But he actually was nameless at first, he only got his name after he killed the entire village he lived in and then later on became a "shinigami" because of his hatred. ._.
And that was the short version of his not so intresting history xD I think I just turned a really sad and horrible story into a joke. Well... Whatever x'D
I hate his feet. D: They just didn't want to look like i wanted them to
Edit: Lololol, my second time uploading this xD Had to fix a small detail in it.