Michiru Sanjou is a secondary character in Attack No. 1, initially introduced as one of the Japan Best Twelve, a select group of top volleyball players. She first appears acting in a hostile manner toward the protagonist Kozue Ayuhara and the other members of the Best Twelve. This antagonistic behavior stems from her background: it is later revealed that Sanjou was the only strong player on her previous team, which never advanced far in championships. As a result, she developed a fiercely competitive and somewhat isolated attitude, feeling that she had to carry her team alone. Her role in the story is that of a rival and later a teammate, as she becomes part of the national-level competition alongside Kozue. Her key relationships are marked by initial friction with Kozue and other top players, gradually evolving as they all work toward common goals in international volleyball. Her notable abilities are not detailed in depth, but her selection to the Japan Best Twelve indicates she possesses high-level volleyball skills at a national standard. Her development, while limited in the available information, shows a shift from hostility to a more cooperative stance within the team context.