Warning: Blog contains a sensitive subject.
The earliest flashback we ever got from Gin and Matsumoto, is when young Gin witnessed Aizen’s men allegedly taking reiatsu from the unconscious Matsumoto. But some people actually theorized something darker – that Matsumoto was raped by Aizen’s men.
Now this may be too dark for a Shonen anime, but some Mangaka have gotten away with dark undertones just by giving vague hints. And I do believe Kubo was no exemption. Here are some examples:
One was the most famous quote that Gin uttered before his death: "If you were to turn into a snake tomorrow and begin devouring humans, and from the same mouth you started devouring humans, you cried out to me 'I love you,' would I still be able to say 'I love you' the same way I do today?"
Now for me what this meant was that Gin did not want Matsumoto to be consumed by vengeance or despair from what Aizen’s men did. Instead, he allowed himself to be the avenger, symbolized by him being constantly referred to as a “snake” by some characters, most notably Rukia. And whether it was his intention or not, Gin saw that Matsumoto did live a normal life. She was not consumed by hatred for what happened to her.
It’s a tragic irony, if you think about it. While he was so bent on making Aizen pay, the one he was avenging has learned to move on.