Mitsuru is part of Wataru's class and seems to be popular with the girls. After being said that he was the one who started a rumor about a ghost and going into an abondoned werehouse, he ends up being kidnapped and beaten up by bullies from his school.
Wataru comes to his rescue and witnesses Mitsurus wizard powers, he summoned some sort of demon to put the bullies asleep.
Mitsuru tells Wataru about the existance of Vison and goes in a journey to fufill his own wish...Little is known about him but he is shown to be a very powerful and often reckless wizard, burning down forests and killing innocent people to reach his goal.
In the end we find out Mitsuru lost his whole family and that his wish was to bring his little sister, Aya, back...He ends up making a mistake and ending his life in Vision.
Right in the last moments of the movie, when Wataru is back to his normal world, we can see Aya and Mitsuru alive and well and Wataru running towards him, probably to hug him...