One popular garp fanfiction story could be about Garp's early days in the Marines, his training and the friendships he formed. Another might focus on his relationship with his family members in a different light, like how he interacted with his grandson Luffy during Luffy's childhood. There are also stories that might explore Garp's role in some of the major events in the One Piece world from a different perspective.
One of the main themes is the search for identity. Garp is constantly trying to figure out who he is in the complex world around him. Another theme is the role of family. His family relationships, including his relationship with his mother, wife, and children, are full of love, conflict, and growth. Also, the idea of gender roles is explored, as Garp interacts with strong female characters and navigates through a society with certain expectations of men and women.
Prince Li Chengqian did not die in the series. In the 23rd episode of the TV series " Celebrating Years," Prince Li Chengqian was kidnapped by Qi Heng's henchmen, but was finally rescued in time by Fan Xian and others. Therefore, Crown Prince Li Chengqian did not die in any of the episodes.
Well, without actually reading the 'ace whitebeards garp hits you fanfiction', it's hard to say for sure. But generally in One Piece fanfictions, it could be about battles, relationships, or character development. Maybe it shows Ace and Whitebeard facing off against Garp in an epic showdown, or perhaps it delves into their backstories and how they interact in a new, fictional situation.