One possible storyline could be that Ace's death shatters the crew's morale, and Whitebeard, in his attempt to avenge Ace, faces an overwhelming enemy. In the fanfiction, Whitebeard might use his last bit of strength to protect the remaining crew members, leading to his own death. Maybe there could be a flashback of their relationship, how Ace was like a son to Whitebeard and how that bond drove Whitebeard to fight to the end.
In fanfiction, the death of Ace and Whitebeard could lead to a new era of piracy. The crew members left behind might form new alliances or go their separate ways. Some might become more ruthless in their pursuit of power, while others might try to uphold the values that Whitebeard taught. The Marines might also take advantage of the situation, tightening their grip on the seas and trying to root out any remaining pirates associated with Whitebeard.
Their relationship can be shown as a father - son type. Whitebeard being the protective and wise father figure, always looking out for Ace. For example, when Ace is in a fight, Whitebeard is there to back him up or give him advice based on his own experiences.
Izou is also a popular character in these fanfictions. His skills as a swordsman and his unique personality make him an interesting addition to stories. He might be involved in adventures with Ace or be part of a sub - plot. Thatch is another one. Since he was the cook, there could be fanfictions that involve him cooking special meals for the crew, including Ace, and there could be some friendly banter between them.
No, it's not likely to be a popular genre. Spanking - related fanfiction in general is a very niche and often not mainstream. And when it comes specifically to 'ace whitebeard spanking fanfiction', it's probably only appealing to a very small subset of fans who are interested in this particular and rather unusual take on the Ace and Whitebeard characters.
I'm not entirely sure specifically what that particular 'ace whitebeard spanking fanfiction' is about as it could vary greatly. It might be a fan - created story within the context of the Ace and Whitebeard characters where some sort of spanking - related scenario is imagined. However, this could be a very niche or even a rather strange and unorthodox take on the characters in the fanfiction world.
One popular ace whitebeard fanfiction might be those that explore their relationship as a father - son like bond. In many of these stories, Ace's growth under Whitebeard's protection and guidance is depicted. For example, there could be a story where Ace overcomes his inner demons with Whitebeard's encouragement.
One great 'ace whitebeard fanfic' could be the one where Ace has to prove himself to Whitebeard's crew. He goes through a series of challenges that test his loyalty and strength.
Some One Piece - dedicated forums may also have user - shared 'ace whitebeard fanfic'. These can be a bit more niche but might have some hidden gems. You can engage with the community there to find out more about these fanfics.
I really like the fanfictions that involve Ace, Whitebeard and Sabo. They are such interesting characters. In many of these fanfictions, the relationship between them is explored in great depth. For example, how Sabo copes with having Ace as his 'brother' again after thinking he was dead. And Whitebeard's role as a father figure to them adds another layer of complexity and warmth to the stories.