When we think about One Piece characters, we are used to considering, for example, the Admirals, the Yonko, the Shichibukai, the members of Revolutionary Army and the strongest ones we’ve ever heard about.
On the other hand, if you reflect just for a minute and you start thinking about those characters who we are used to seeing since the first episodes, there’s one in particular who is even more mysterious than you think: he’s Garp.
Garp is a vice-Admiral who is rejecting since years the offer to become Admiral because he doesn’t want so much responsibility; anyway, we know for sure that in the past he had been able to fight against Gol D. Roger and Shiki The Golden Lion and, for this reason, he’s now nicknamed “The Marine hero”. Despite this, we’ve never seen him in an all-out fight.
Even during the Marineford war, while everyone was on the battleground fighting quite seriously, Garp didn’t fight, although he’s a vice-admiral. This seems really strange, doesn’t it?
Suddenly, at a certain point, we saw that Marco tries to save Ace, Sengoku sees him and gets ready to engage the fighting, but Garp unexpectedly jumps and punches Marco; astonished, Sengoku exclaims “nobody told you to jump in on your own Garp!”. We all know that Marco is stronger enough to fight against the Admirals, but after suffering that hit by Garp he had to give up with his attempt to save his friend, although the Garp wasn’t using the Armament Haki.
From this scene we can understand how powerful could be Garp; in addiction, we also know that he uses mountains as punching bags and that he’s able to send back to his enemies the cannon balls they shot just thanks to his fists, and without using the Armament Haki.
Furthermore, when Akainu killed Ace, Garp started walking nervously towards the Admiral and Sengoku stopped him in a really violent way.
So, at this point, what could be Garp’s real powers?
In my opinion, he possesses an advanced type of Haki which could possibly not manifest externally, despite being incredibly powerful; moreover, we don’t know anything about the possibility for him to have eaten a Devil Fruit, since to fighting against Roger and Shiki it’s difficult to think that he only based his skills on physical strength and Haki powers.
In fact, Sengoku reproached that way Garp because he didn’t want him to start a war against Whitebeard, since it would have definitely destroyed the whole island; Sengoku also stopped Garp so roughly because he was afraid that Garp could kill Akainu, and we know that Akainu is not a weak enemy to deal with.
In conclusion, I’m convinced that each person who saw at least one time Garp fighting seriously knows how strong he is and knows how dangerous could it be if he would give his best; for this reason, Garp is Marine’s last card to be used only if there’s no other choice. We don’t have to forget that his complete name is “Monkey D. Garp”, so that his “will of D.” could be strong enough to make him as powerful as Roger, Shiki and also other amazing characters such as, for example, Shanks, Whitebeard and Sengoku.