Sugata does not want Wako to be chained to her "fate" as a Miko simply because she was born as one. He sees Takuto as an outsider who will eventually leave the island to return to the mainland. He hopes that by setting her up with Takuto that he can take her away from the island, and away from her preordained role in life.
As the prince who will inherit the power of the royal Cybody, Sugata wants to take all the responsibility of protecting the island's secrets himself. He wants to be the only who suffers, sacrificing his own future and freedom to allow others to life their lives as they please.
What Sugata does not expect is that Takuto is not just any outsider, nor is he the type to stand and watch as he tries to be the noble hero. Takuto has his own secrets, and his own past. His father and grandfather are very much a part of the secrets of the island, and Takuto himself knows a fair bit more than he's letting on.
Sugata will have to stand and watch helplessly as Takuto not only intrudes into his life, but also takes the role of hero away from him, showing him that one does not have to sacrifice himself or try to artificially create a better future for other people. Takuto will prove that each person can stand up for themselves and that even though something might be decided before they were even born, it doesn't mean that they don't want to do it. Wako might not have been given a choice in becoming a Miko, but she is just as willing to stay and fulfill her role to protect her friends, and Sugata should accept that.
That's what I think anyway.
