I'm reading the novel and so far no rival has been introduced. It might also help that the captain is completely cold towards all women with the exception of Sei.
Where do you read the novel?
The web novel's links can be found here: https://www.novelupdates.com/series/seijo-no-maryoku-wa-bannou-desu/
The light novel can be found here: https://www.novelupdates.com/series/the-power-of-the-saint-is-all-around/
Thank you
No fiance does not mean no rival. Something is gonna happen.