I feel like he's less of a rival but more of a character that would push Misuzu into becoming better and to gain courage to make things right. A lesson if you'd like. To him(Sanada), what misuzu is doing is just something he's doing to appease himself so that misuzu can move forward with his life.
Perhaps this incident would make misuzu learn that clearing things up and speaking up for himself is important to ensure he would no longer be misunderstood, and that staying quiet while he waits for the "right time" could lead to further misunderstandings and even more painful situation.
I feel like he's less of a rival but more of a character that would push Misuzu into becoming better and to gain courage to make things right. A lesson if you'd like. To him(Sanada), what misuzu is doing is just something he's doing to appease himself so that misuzu can move forward with his life.
Perhaps this incident would make misuzu learn that clearing things up and speaking up for himself is important to ensure he would no longer be misunderstood, and that staying quiet while he waits for the "right time" could lead to further misunderstandings and even more painful situation.