During the Dressrosa arc, we saw that Usopp, who has always been considered as a foolish and weak character, has awakened the Observation Haki and, thanks to it, he saved Luffy and Law and he gave the opportunity to everybody to take their revenge on the Donquijote Family.
Despite the fact that, of course, as we know Usopp isn’t the only character in the series who is able to use the Observation Haki, I’m strongly convinced that he is the owner of the most advanced form of this ability among all the characters we saw until now.
Why? Let me explain it to you!
Since the early beginning of the series, we have always seen Usopp as a liar who used to lie in order to let us know that he was afraid of something; further, we also saw that he continued lying to Kaya in order to cheer her up.
Despite this, since those episodes, many of his stories started to become true, even after a very long time, such as, for example, meeting a giant goldfish, fighting against a giant mole, meeting dwarves and being a captain; those were all facts told by him which started to really happen during the story, from some episodes later to the more recent Dressrosa arc.
Well, since Oda has never given us any proof of the existence of “coincidences” in One Piece, I don’t believe that Usopp invented them and then they really happened by chance; on the contrary, I believe that he had already seen them before their happening thanks to his visions, which already were a kind of “lite” and “unconscious” Observation Haki.
Of course, he couldn’t predict when they were going to happen, he could only predict that they were going to happen and, as a child, he confused his predictions with something like childish imagination and fantasy.
We know that Observation Haki users can develop their skills to such a level that they can seemingly predict the future, as we saw in Charlotte Katakuri’s case; moreover, also Madam Shyarly and Basil Hawking are able to predict the future by using some objects: Shyarly uses a giant crystal ball and Basil uses cards. For this reason we could think that maybe also Usopp will use an object in the future; on the other hand, it’s also possible that he just awakened his special Observation Haki thanks to his focusing ability and to his sniper glasses and now that he achieved using it, he’s able to use it even without any object.
In conclusion, we don’t have to forget that Usopp is the son of Yasopp, one of the most trusted friends of the Yonko Shanks and the sniper of the Red Hair Pirates; for this reason, we could presume that Yasopp is very strong and that Usopp will inherit at least a part of his father’s strength.