From time to time Shigurui reminds me of Baki, a series which I also love deeply. Sometimes it's because of character designs, sometimes the way both authors drow muscles and veins... and sometimes by some insane training methods or dedication.
Gonza outdid himself on that last part. I guess "I'm weak, if I just break up with her, my dick might eventually send me to her or another lady again - I can't be chained by my instincts like that" was the thought he had - or well, more or less.