the role of being a partner of someone
相手役になる人
a person who occupies a responsible position
in Noh, a supporting role
〜の役
the role of being in charge of (something)
a person who is in charge of (something)
the host
a person who occupies a responsible position
貴婦人のお相手役
the role of being a personal attendant to a nobleman or noblewoman