Majora's major role in the anime is to be there for his fellow Scarf Heroes when they feel down. With his passion in helping others, and his optimism, every person he helps feels a sense of joy. He defends them when they are weak or brittle, and he represents what this group stands for. Alyssa has seen the true potential and good characteristics Majora has, and quickly had asked if he would like to join. He vows to protect and defend the dignity of every human being, and generally improve the lives of others. After he had made those promises, he continues to do that to this day.
At some point, it will later be found out that Majora is Alyssa's step brother
During Majora's journey it will also be found out that Majora has a brother that he not only doesn't remember, but has an insanity state similar to that or Alyssa. (insanity is in the family it seems) sadly, his unstabele mind will by the end of the journey Majora will be forced to kill his brother.
And to top it all off it will also be discovered that Majora has not developed his family "inheritance" as it were because of something his brother did to him when they were young that damaged his soul which (when he found it) the aura of his sword Vahnhashiron fixed up and more.
The biggest part to all that is that Vahnashirons presence is required to keep him as he is, so much so in fact, if the sword were to move too far away from him, (VERY far) or if it's jewel were to be destroyed it would flat out kill him. Although if the jewel were destroyed it would not only kill him but it would also greatly effect everyone memories of him, but these last little details of how much Majora requires his sword, will remain unknown to him.