I think Akio's pretty manly, but I don't think he can compare to Nagasumi.
If there's anything I pride most in GAR characters, it's a change of heart. And Nagasumi started off the story as a fag - rather, a weak, normal human who comes into fortune with a magical waifu he doesn't deserve. AND HE KNOWS IT AND DIDN'T WANT HER.
Yet, over the course of the story, he developed a sense of duty/desire to protect her and gradually they truly did fall in love. Even with powerful strong guys like Goza, Shark and Masa around, there were still dangers that Nagasumi had to deal with.
And after fighting with them and surviving, he managed to become powerful enough to protect San himself and earned his place as one of the yakuza. AS A NORMAL HUMAN (not so normal anymore but.).
That's the story of how a boy becomes a man, the archetype story of a fag going GAR. I love Akio, he's a really cool dude and like a father, but in the end he's still basically like a big kid, so he's a bit weaker.