If you're looking for manga similar to LegendZ, you might like these titles. All recommendations are made by Anime-Planet users like you!
Reiji Ozora, a high-school student who excels at nothing, tires of every game he's played - that is, until one day his friend Maiko introduces him to the world of Dragon Drive. In it, players are given virtual dragons to ride and fight against one another; though unfortunately for Reiji, he's assigned to a small dragon with unknown attributes. Determined to increase his skills, Reiji soon jacks in to a training program when suddenly he, Maiko, and a boy named Daisuke are transported into another world called Riyku! In this new foreign land, not only must these friends try to find their way home and fulfill what is asked of them, but Reiji must also discover the truth behind his dragon's abilities.
Both of these mangas are about a game which revolves around dueling with virtual monsters, yet in both stories the monsters turn out to be more than just virtual creatures. Additionally, both series feature some big company with dark designs, who try to use the creatures to their own ends. Lastly, there is a very close resemblance in the artwork as well. These two series have so many similarities that you would swear they were actually 2 parts of the same series.
They both revolve around kids and virtual dragons/mythical creatures and have similar plot lines. If you liked one, you'd definitely like the other.