Akainu is father of Hibari.
Papasuzki knows Bonney's backstory, and didn't have the heart to murder Kuma while knowing the truth about him.
Look at Akainu's dialogue here: we never see him this reflective in battle/post battle.
Akainu is clearly feeling sorrow for Bonney here.
"You're just a damned puppet now" hits different when you look at Akainu's frustrations in the New World and with the Gorosei.
Akainu spent a ton of time in Marineford trying to get Jinbei to stand down and surrender Luffy, because Akainu respected Jinbei as a reasonable man who had worked hard to prevent the negative effects of piracy.
Akainu clearly knows about Kuma's past based on this dialogue; Papazuki spared Kuma.