As for Mashiro...
Put it this way: the reason Rita had been able to explain her unreliable ideals to Sogo Doma without getting verbally demolished into tears was because he took into account that she had looked after Mashiro for so long without getting upset over it. Even he was occasionally left speechless by Mashiro. If he hadn't promised to take care of her, he@#$...
Take now, for example. It wasn't that Sogo Doma had to be so resolute—if he showed even the slightest hesitation, Mashiro really might give up studying!
"Setting everything else aside..." Sogo Doma continued explaining, "isn't your manga set at a school too? If you give up studying, then your later plot..."
"..." But Mashiro did have the virtue of accepting advice. "That's true. Then I won't give up studying."
"See?"
Sogo Doma pressed the advantage. "Even an idiot like you, Mashiro, who neither likes studying nor gets good grades, wouldn't give up studying. What right do those people have to say they'll give up drawing just because they aren't as good as you?"
"..." Mashiro was silent for a while before she said, "Sogo, were you badmouthing me?"
"How could I be?"
"I'm not stupid..."
"If you're not stupid..." Sogo Doma smiled. "Then why are you blaming yourself for other people's cowardice and mistakes?"
"But Rita..."
"I know..." Mashiro had barely started speaking when Sogo Doma cut her off. "To you, Mashiro, Rita is irreplaceable. Honestly, aside from blaming you for her giving up painting, there isn't a single thing anyone could fault about how well she's treated you..."
"Then..."
"But sometimes, being good to someone isn't necessarily a good thing..."
"Why?"
"..." Because she'd gone too far—if she hadn't spoiled you so much, you wouldn't even lack common sense! Sogo Doma really wanted to