Every five hundred years, the Shaman Fight takes place to choose the Shaman King - the strongest of the shamans. Now, the time has come once more for the Shaman Fight, and shamans from around the world have gathered in modern-day Tokyo to compete. One such competitor, Yoh Asakura, is determined to become the Shaman King. Together with his friends and his partner spirit, Amidamaru, Yoh sets forth on a journey to decide who is the strongest and most worthy to become the Shaman King.
Both of these shounen manga involve people of all ages who fight against one another using power beings as weapons. The art style is also the same because it's done by the same person. Fans of one would love the other for sure.
The plots of Shaman King and The Violinist of Hameln each center around a group of friends who meet along the course of their journey. In both mangas, the primary goal is to prevent the antagonist/s from destroying humanity. Both use of spirituality as a plot device, though SK makes use of Buddhism and nature while VH takes on a Judeo-Christian tone. Finally, the endings of each take on a similar quality - although that's something the reader needs to judge for himself.