Garp gritted his teeth, not knowing what to do.
He'd devoted his entire life to the Marines, to fighting pirates. It even went so far that his only son wanted absolutely nothing to do with him, only consenting to see him once a year for his birthday because he knew Garp would just show up anyway, so he might as well set a place and time to ensure Garp stayed away from his current hideout. Rescuing and hiding Ace from the Marines search for him when he was born was the most rebellion he'd ever done against the organization he lived for.
He'd tried to raise Ace to be a Marine, tried to raise Luffy to follow the same path. He'd ultimately failed there, with both boys choosing piracy instead. He would have settled for them both settling down and choosing an honest profession, but instead they chose a life of piracy.
After that, he'd turned a blind eye whenever he knew Ace or Luffy were nearby, well except for when he met Luffy at Water 7.
All small acts of rebellion as far as he was concerned, if that.
But now... now his grandson was up for execution.
He didn't know what to do here.
Protect his family? Or the justice he'd upheld all his life?
When The Phoenix flew up to try and save Ace, he moved almost without thinking, and knocked the pirate out of the air, back towards the ground. Then when Luffy was right in front of him... he raised his fist to knock him down too...
But he just couldn't do it.
He couldn't raise his hand to Luffy, not here, not like this.
So he let Luffy hit him, instead.
When Luffy succeeded in getting Ace safely off the platform, he crumpled in relief, and opted to stay where he was, pretending to have been knocked out, although he was pretty sure Sengoku knew otherwise.
He silently cheered his boys on, hoping they got out of here, only to stiffen when Akainu reappeared and started taunting Ace. Say what you like about Akainu, but he sure knew how to read his opponent and get inside their heads. Just look at what he did with Squard, getting him so worked up that he attacked Whitebeard. Although, getting inside Ace's head wasn't too difficult right now, everyone knew that Ace rarely, if ever, ran from a fight, especially once you started taunting his family.
Most of those people, though, also learned why that was a bad idea.
But... this was an Admiral Ace was standing in front of, he'd just spent several weeks in Impel Down, and when he was handed over to the Marines in the first place he was practically half-dead, he hadn't received medical care since then, instead only accumulated more injuries while in prison.
He wanted to yell, wanted to scream at his hothead grandson, wanted to run and get between the two of them... but he couldn't. He couldn't move, he still didn't know which to protect. He knew that he might as well have made his choice when he allowed Luffy to get by him, but...
When Akainu struck the killing blow, and Ace died in Luffy's arms... and he watched his youngest have a mental break-down...
Why was he so useless?!
What did the Marines matter?!
This was his grandson, his family.
HE KILLED HIS GRANDSON!
He didn't know what happened, but the next thing he knew, Senny was holding him down, yelling in his ear for him to get a hold of himself.
He was relieved when Shanks arrived and stood between the remaining Marine forces and the pirates who were trying to fulfill their captains final order and escape. (Later, after he calmed down enough to ask what happened when after Ace was killed, he would be very, very proud of protege, not only had he unlocked a very powerful talent with Observation Haki, but he stood up to Akainu, although hearing that Akainu tried to kill his protege too, just made him even angrier.)
He was relieved when Luffy showed up with Jimbei and Rayleigh to ring the Ox Bell and pay a tribute to the fallen, because it meant he wasn't dwelling on Ace's death, and he was alright.
He was done with the Marines, though. He was considering finally retiring from active duty, maybe train new recruits instead on occasion, but he was done.
Both his adopted grandsons were dead, it was just him, Dragon, and Luffy left.
Well, at least he knew what to do now, if he ever ended up in another situation like this, he wasn't going to fail his family again.