Tang San is a really popular choice. Since he is the main character in the original Douluo Dalu, being reincarnated as him allows for a lot of interesting twists on his story. Another popular one is Xiao Wu. Reincarnating as her can lead to different perspectives on her relationships and her role in the story. Also, characters like Dai Mubai are often chosen as well. His powerful soul and his status as a prince make for an exciting reincarnation scenario.
Reincarnating as Midoriya but with some changes in his quirk manifestation could be fascinating. For instance, what if instead of getting One for All in the normal way, the reincarnated Midoriya discovers a different way to unlock and use the quirk? This could lead to a whole new set of adventures and challenges, and also a different dynamic with the other characters.
Well, of course, Goku is a very common character. Since the story is about being reincarnated as a Saiyan, Goku's presence is often there either as a mentor or as a benchmark for the main character's power level.
I really like 'A New Beginning for Harry Potter'. In this fanfic, the reincarnated Harry has a different perspective on his role in the wizarding world. The story dives deep into his relationships with the other characters like Hermione and Ron, and how he tries to prevent some of the tragedies that happen in the original series. It's a great read for any Potter fan.
According to the paragraph of information given, there were no books that met the requirements for recommendation. It was suggested that he read more online novels before looking for suitable recommendations. I hope you like my recommendation.
One common theme is self - improvement. The OC, with the help of the system, usually tries to become stronger, whether it's in terms of physical abilities, magical powers or knowledge. Another theme is exploration. Since they are in a new world, they explore different places, cultures and meet new races. For example, in many such fanfictions, the OC might explore a hidden dungeon or a lost city.
One interesting plot could be the protagonist using their modern - day knowledge to change Sakura's fate in the Naruto world. For example, they might help her become a stronger ninja earlier by introducing new training methods.
One popular theme is self - discovery. The reincarnated OC often has to figure out who they are in this new life, especially if they have memories from their past life. Another theme is changing fate. They might try to avoid the same mistakes or tragedies that happened in their previous existence. And the theme of power acquisition is also common. Maybe in their past life they were powerless, but in the new reincarnation, they strive to gain strength and influence.
At first, the character might be confused and scared, having to adapt to a new and very different body. As time goes on, they would start to learn the instincts and abilities of the dinosaur. For example, if they are a T - Rex, they'd learn to hunt and use their powerful jaws effectively.
The sword itself is often a very popular character. After all, it's the center of the story. Readers are interested in its thoughts and growth throughout the reincarnation process.