If Law of Ueki is PG then Law of Ueki Pus is more PG-13. There a noticeable more gore factor with in the expanded series. A new set of character friends to help him fight in a new world. Ueki also has none of him godly weapons in this series and simply starts fresh. Also I think there is a more noticeable romance factor with in the story. Note: pay attention to the 1st chapter the mangaka gives you a clue to the end of the series.