He is a creep since he's constantly hanging around even when his friend isn't home. No one with more than 2 brain cells would fail to notice this and confront them about it.
Not only is it just one match, its a match that they don't actually have to play because they've already qualified for the nationals. Its literally just being done to satisfy Nagisa's ego because she can't stand the thought of playing alongside her without first settling a grudge from a match...
Ship isn't sunk yet, but does the author really have the balls to go full yuri incest? At this point who knows, they keep throwing nonsense out every chapter. This twist would somewhat explain why they were so attracted to each other in a short period, but probably doesn't explain them making...
What doesn't make sense is why his family, who has the goal of wiping out the Hyullas, would go through all this effort to keep him locked up instead of having him breed with as many supreme Hyullas as possible.