What is Dragon’s secret and why is he being held back? I think the answer lies with his tattoo.
It’s actually quite an easy tattoo to understand if we take the most flashiest part out of it, the lines. We actually have seen these lines on many occasions and they symbolize “containment”.
We see this for example with Ryuma and how a message was contained in identical lines to Dragon’s tattoo. Basically, 4 lines in form of a square are used to contain a message within it. We see this in other anime like the Gotei in Bleach.
Hence why we can safely discard the lines and focus on what is contained within them, red cubes.
The angle when the first Road Poneglyph was introduced looks 2-dimensional, this is similar to Dragon’s cubes, who are also 2-dimensional. That is a weird way of illustrating Poneglyphs to say the least and I estimate it is a hint to Dragon’s tattoo. Can it really be that Dragon is related to Road Poneglyphs? Almost certainly, his entire path of taking down the World Government is a kin to Luffy’s and as a follower of the “Will of D” he is connected to them already. He is also aware of the true face of the World Government and defined the mentality of “the night” that the One Piece world is metaphorically suffering under.
Of all the characters who have no obvious relations to the Roger Pirates, Dragon seems to be the most woke guy alive. Rebels think so and have joined him in a battle for freedom. The Revolutionary Army is probably the biggest “private army” lead by a single individual on the whole planet. No kingdom, country and even the government by definition can say that. Even Robin was drawn to this figure and wanted to meet someone with that kind of flare. Wait, did I say “Robin” when we were talking about Poneglyphs?
Not only did Robin meet Dragon but she is a fundamental part of the revolution or at least that is how Dragon sees it. The Ohara incident seemed to have sparked the rebellion in the first place because Robin is called the “Flame of Revolution”. Dragon searched for the one person who can decipher Poneglyphs for over ten years. The connections are there but there are more long-term clues that we couldn’t appreciate at the time.
Dragon ignores the question when Koala inquires if Dragon knows about “Drunken Iron Ore”. Why is this important? Well, the material is almost certainly what Poneglyphs are made of. Koala says that only a small number of countries can produce weapons with it and Wano is known for its blacksmiths and of course the creation of the Poneglyphs.