It's popular because it shows a different side of their relationship. People like to see Luffy being more than just his usual carefree self and using his smarts in relation to Nami. It adds depth to their dynamic.
He might try to self - medicate at first. Maybe he takes some experimental drugs he's been working on in his lab. After all, he's always been one to take matters into his own hands.
Well, it definitely slows him down. He can't push himself as hard as he usually does. His stamina is lower, so he might not be able to complete his normal training routines.
It's popular because their relationship in the original story is really interesting. Luffy is the carefree and determined captain, while Robin is the intelligent and mysterious archaeologist. Fans like to explore more about their potential interactions.
In the One Piece world, Luffy is on this grand adventure and Hancock is a powerful figure. Their relationship has this allure of the unexpected. Fans are drawn to the idea of these two very different characters coming together. Fanfic writers can play with their personalities and create all sorts of interesting scenarios. For example, Hancock's initial haughty attitude towards most people but her special soft spot for Luffy makes for great storytelling. It's also about the idea of love in a world full of pirates and battles, which is quite appealing.
The reason the Qing Emperor was afraid of the box was because it contained the Barrett Heavy Sniper Rifle. This was the ultimate weapon left behind by Ye Qingmei. The Qing Emperor had personally witnessed the power of the Barrette. He had witnessed Ye Qingmei use the Barrette to kill two princes who were qualified to inherit the throne. The Qing Emperor knew the Barrette's long-range killing ability. Even if he was a martial artist at the Great Grandmaster level, he could not block the attack of this weapon. Thus, the Qing Emperor was filled with fear of the chest. He was afraid that the Barrette in the chest would once again threaten his life. In order to fight against Barrette, he often researched and made arrowheads and heart-protecting mirrors, hoping to find a way to resist the threat of such terrifying weapons. The Qing Emperor's fear stemmed from his memories of Barrette and his fear of Ye Qingmei. This fear had always troubled him, making him afraid to leave the Royal Palace.