"One day a king was going somewhere" is a bit vague. It would be clearer and more interesting as something like "One day, a king was travelling through the city/countryside ...". Note the comma after "One day".
I would connect the first two sentences as they are very short and choppy. "One day, a king was travelling through the countryside when he saw a large group of slaves". Note that "a large group of slaves" is much more natural than "a group of many slaves".
The next two sentences don't fit well together. Until we read the end of the story it doesn't make sense that the king would kick someone he liked. That's not normal behaviour. I would say something like "One slave caught the king's attention and he kicked the slave very hard".
I would connect later sentences too: "The king smiled (you don't need "happily" here), bought the slave and immediately set him free".
At the end, it's not clear whether the spirit of freedom is still alive in the king or in the slave. Logically, we assume it's the slave but in the rest of the piece, "he" refers to the king.
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