In these fics, Sakura often becomes badass through intense training. She realizes that she needs to be stronger to change things in Konoha or to prove herself. For example, she might train under a mysterious master or in isolation, like in 'Sakura's Solitary Training' where she spends months alone in the forest, honing her skills.
Well, Vegeta would be a likely character. He might be initially suspicious of the female Goku. Maybe he thinks she's a threat or just can't believe there's another Goku - like being. He could be there to add some comical moments as he tries to understand the situation.
One great book with badass fictional characters is 'The Lord of the Rings' by J.R.R. Tolkien. Characters like Aragorn are badass. He's a skilled warrior, a natural leader, and has the courage to face the dark forces of Sauron. Another is 'Harry Potter' series by J.K. Rowling. Harry himself is a badass as he battles the powerful and evil Voldemort throughout his life at Hogwarts and beyond, not to mention his friends Hermione and Ron who are also very brave. Then there's 'The Hunger Games' by Suzanne Collins. Katniss Everdeen is extremely badass. She volunteers for the Hunger Games to save her sister and shows remarkable survival skills and defiance against the Capitol.
Well, it could be characters like Draco Malfoy. In the original series, he had his moments of growth and in fanfics, he might be one of the main Slytherins to defend Hogwarts. Maybe he finally realizes the importance of the school and his own values change. He could be joined by other Slytherins who were perhaps overlooked in the official story but show their true courage in the fanfic.
In some fanfictions, Snape has badass moments when he outsmarts Voldemort. For example, he manages to mislead Voldemort about the location of a crucial magical artifact. He uses his Occlumency skills to his advantage, hiding his true thoughts and intentions while presenting false information in a very clever way. This not only shows his intelligence but also his courage as he risks his life to deceive the Dark Lord.
In general, it's a bit of a toss-up. The strength of Manga Goku and Anime Goku can vary depending on the specific arcs and battles. Sometimes, it might seem like one is stronger in a particular situation, but that could change in another.