Akainu has a grudge against Luffy and Dragon. Luffy feels the same way. After all he was responsible for Ace's death even more so than BB was. I don't know how things will go down, but Sabo might get involved somehow. Akainu is extremely dangerous opponent for Sabo to defeat alone. It may just end up being a small fight. But it will be Luffy who takes him out in the end.