Well, in many fanfictions, a common storyline is the training Ace received from the Whitebeard pirates. It shows his growth within the crew. Also, there are stories about their feasts and celebrations on the ship, which give a sense of the crew's camaraderie. Some fanfictions even create alternate universes where the Whitebeard pirates and Ace face different challenges not in the original story.
Some fanfictions revolve around Ace's past and how the Whitebeard pirates helped him come to terms with it. There are also stories that center on the loyalty within the crew towards Ace. For instance, how they would go to great lengths to protect him. Additionally, the idea of Ace's role in the crew's future plans is a popular theme, like how he might have led the crew in certain situations had things been different.
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.
One interesting story could be about Ace's adventures before joining the Whitebeard Pirates. Maybe he has some encounters with unique sea creatures or discovers a hidden island. Another could focus on his relationships within the crew, like his bond with Marco. There are also fanfictions that might explore Ace's training under Whitebeard and how he grew stronger.
One interesting storyline could be Fem Luffy joining the Whitebeard Pirates on a special mission. Maybe they have to rescue a kidnapped crewmate from a powerful enemy. Her unique abilities as a female version of Luffy, like her stretching powers, could play a crucial role in the rescue.
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.
The element of sacrifice also often comes into play. The Whitebeard Pirates in these fanfictions are willing to sacrifice their own interests, whether it's a share of treasure or their own safety, for Ace. For example, in a battle - heavy fanfiction, a crew member might take a critical hit meant for Ace, showing just how far they are willing to go to protect him.
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.
Whitebeard himself is often a very popular character in fanfiction. His powerful presence and fatherly role in the crew make him a central figure. Writers can explore his leadership, his past battles, and his relationships with the other crew members.
One great fanfiction could be 'The Whitebeard's Vow'. In this, the Whitebeard Pirates are extremely protective of Ace. They show their loyalty and care through various battles and situations. For example, when Ace is in danger from other pirate crews, they form a tight shield around him, with each member using their unique abilities to fend off the attackers.
I think Ace is the top choice. His internal struggle between his loyalty to Whitebeard and his past with Gol D. Roger is a goldmine for fanfiction writers. But we can't forget Jozu either. His strength and his unwavering loyalty to the crew are aspects that can be developed in interesting ways. And Vista, with his swordsmanship, can be a really cool character to write about in relation to the crew's battles.
One interesting Whitebeard Pirates fanfiction could be about a new crew member joining them. This new member has a unique power that the crew has never seen before and they have to figure out how to incorporate it into their battles and daily life on the ship.