The fact that he couldn't be proud with his own chosen path is the biggest flaw of Kiritsugu. From hindsight, I admire criminals and villains that they could just follow their heart's desire and don't give a shit even if it meant horrible consequences. How many of us could actually do or accomplish what we wanted? Kiritsugu regretted every step he takes, and that is simply not something human is designed to endure forever.
Btw, my answer would be my loved ones first of course. Hardly a hero stance, but that's what it means to be human. And sometimes being human can be more heroic than any hero will ever be.