Saitama's strength in the manga comes from his intense training and unwavering determination. He pushed himself to the limit every day, which eventually led to his overwhelming power.
Well, kangaroos have strong legs because they use them a lot for hopping. They start as babies and keep practicing, and over time, their leg muscles grow really big and powerful. Also, their diet helps give them the energy they need for all that jumping.
You can start by finding a reliable source to access the Baki manga, like authorized online platforms or physical copies from bookstores. Then, just start from the first volume and enjoy the story.