I knew it! The quints' father was going to use Takeda to re-assert his authority over them. Bad mistake. Now they've got additional motivation to achieve high grades, just to spite him. Honestly, he has limited leverage over the quints, simply because they're living on their own and paying most of their own living expenses.
The quints' secret weapon in all this is, that each of them tutors the others in what they do best in. Futarou is not to be underestimated. We've seen what he can do when he's motivated by challenges to his pride. Takeda is going to get mulched by the Futarou express on the way to top 10 National ranking
It's going to get really tense within the family, once the girls become legal adults. Dad still tries to re-assert parental authority over them, and they say fuck off, we're adults now!