SR is a great character, no doubt
... immensely likable.
However, making her the main character - like several people demanded - would be a disastrous mistake. What makes her appealing next to her kindness is her openness. What you see is what you get. However, this is also tremendously limiting in storywriting. A storyline with Haru and SR would turn into a snoozefest in no time.
One particular strength of KYH is the air of mystery which surrounds her. And what I find particularly impressive is that the more you learn about her, the more questions that are answered about her, the more new questions arise. This is her strength, which is keeping the story fresh.
Nope, SR as a great new recurring character and a foil for KYH - perfect. As main character - certainly not.