Misunderstanding and Usopp in One Piece are like a match made in heaven for instance, 'God Usopp' is a perfect example to signify this relationship. From the very start of the series, Usopp has been a character who lied and later became part of the lies he told.
He once lied about a swordswoman who had meat during the Thriller Bark arc. This might have come true as Rebecca during the Dresssrosa arc. So, this could mean that Usopp is not someone to mess up when it comes to making utterly ridiculous lies.
Another such lie was his claim of having an army of 8 thousand soldiers which became true in the Dressrosa arc. But this lie was accompanied by an image that, although it started as a meme later developed into this Straw Hat being considered one of the strongest pirates.
One Piece: Why Usopp is called God Usopp
During the Dressrosa arc, Usopp defeated Sugar and freed everyone from her devil fruit ability. After doing so, he was fatally injured and was carried by Hajrudin toward the people who were freed just now.
Right about this time, Sabo also destroyed the floor of the Colosseum, under which Usopp and the others were present. Light emerged from the top of the basement, shining on Usopp who was being carried by a Gaint, and made him look like a heavenly being. From this point, the dwarfs and other warriors before him started calling him God Usopp.
During the Dresssrosa arc of One Piece, Usopp and Robin tagged along with the dwarfs and the giants to take care of the Doflamingo Pirates Sugar and Trebol. Their plan's premise was to make the enemy eat Usopp's Tatababasco and render them unconscious.
As they progressed with their plan, Trebol and Sugar made their entrance, and Robin had to stop Leo from replacing a grape with Usopp's Tatababasco ball. After this, Robin and some of the dwarfs lured Trebol out of the scene, thus giving Usopp's group a chance to attack Sugar.
Unfortunately, they were utterly defeated and transformed into dolls by Sugar's devil fruit ability. She later ordered them to kill any intruders that were present near her. On the other side, Trebol had also trapped some dwarfs with his devil fruit abilities.
Robin had also fallen prey to Sugar's devil fruit ability, which put all the pressure on Usopp, who was looking for a chance to make an easy escape from this situation. But he was hit with guilt as Leo kept urging Trebol about how Usopp would never run away and save all of them.
On this, Usopp made a flashy entry and told them about how he was only hiding to be deceptive about the enemy. He then asked them to build his statue alongside their hero Noland, if he died while fighting the enemy. Usopp used Midori Boshi: Platanus Shuriken to attack Trebol which ripped him into two pieces.
Usopp got injured after making this move, and Sugar pushed his own Tatababasco into his mouth. In the impulse of the moment, Usopp made a horrendous face, which scared Sugar to the point that she fainted. After she fainted, her devil fruit ability was released and everyone who was transformed into a doll returned to normal.
Hajrudin picked up a gravely injured Usopp and raised him into the air as everyone thanked him for saving them. The top of the basement was also destroyed at the right time, thus shedding light onto Usopp, who looked like a God.
This led to the dwarfs and everyone else present before him calling him 'God Usopp.' As he was very injured, he couldn't comment anything to the people present before him.
He wasn't referred to as Kami Usopp (Kami in Japanese means God) but rather as God Usopp. This signified that him being a God is just a joke or a meme that started from the Dressrosa. He is still referred to as 'God Usopp by the dwarfs of Dressrosa and even Law referred to him as God Usopp later in the series.
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