What are the common themes in 'One Piece Luffy brother OC fanfic'?

In a One Piece fanfic, an OC (Original Character) as Luffy's rival could be really interesting. This OC might have a unique Devil Fruit ability that directly opposes Luffy's powers. For example, if Luffy has the Gum - Gum Fruit which gives him stretchy abilities, the rival could have a hardening or shrinking ability. This would create intense battles between them as they fight for different ideals on the Grand Line.

Friendship is a very common theme. Their unwavering loyalty to each other is often explored. For example, in many fanfics, Zoro will always be there to protect Luffy and vice versa.

One common theme is adventure. Since One Piece is all about adventure, these fanfics often have the original character joining the Straw Hat crew or going on their own adventures in the Grand Line. Another theme could be romance, maybe the OC has a romantic relationship with a canon character related to Hina's story.

One common theme is self - discovery. The oc often has to figure out their place in the One Piece world, which is full of unique cultures and powers. Another theme is friendship, as they usually end up forming bonds with the existing characters like Luffy and his crew.

One great 'One Piece Luffy brother OC fanfic' is 'The New Brother in the Straw Hats'. It adds an interesting original character as Luffy's brother who has unique abilities like being able to control water, which is a new concept in the One Piece world. This OC's journey with the Straw Hats brings a lot of fresh and exciting adventures.

One common theme could be friendship evolving into something deeper. Since Ace and Luffy have a strong bond in the original 'One Piece' story, in these fanfics, it might be explored as a more romantic or intimate relationship. Another theme could be sacrifice, as both characters are known for their selfless natures in the anime.

One interesting plot idea could be the OC brother having a unique power that contrasts with Luffy's. For example, while Luffy has his rubber powers, the brother could have the ability to control metal. This would lead to interesting interactions within the Straw Hat crew, like helping Usopp upgrade his weapons. Another idea is that the OC brother has a different view on the One Piece treasure. He might be more interested in the historical aspect of it rather than the wealth or power it represents. This could cause some internal debates within the crew as they journey towards the Grand Line.

A common theme is the exploration of their family relationship. Given that in the original series, their connection isn't delved into much, fanfiction writers often fill this gap. They might write about how Dragon feels about Luffy's growth as a pirate, whether he's proud or worried.

I haven't really come across many of these, but perhaps themes could include how the crew reacts to such an unexpected situation. Maybe they'd be protective or confused.

The OC brother could fit in as a strategist. Luffy is more of an action - first kind of leader, so having a brother who can think several steps ahead in battles and planning voyages would balance the crew's decision - making. For example, in dealing with the Navy's traps, the brother could analyze the situation and come up with a smart escape plan.