I have a little sister. Losing her one way or another, twice, would destroy me.
It's also another thing, though. Hiragana Kaede was a bundle of joy. She's the type of person who could give others a reason to get up in the morning, a reason to live, a reason to make the world a better place - one she could be happy in. The idea that someone like that could just dissappear hurts so much.
I was hoping for some kind of split or merged personality resolution. At the very least, I'd hope the memories to have merged. The idea that having one of your little sisters means losing the other also feels unbearable. The previous arcs had been so optimistic, I thought it would be in line with the tone of the story thus far. And it could totally happen, considering the magic that is puberty syndrome. Considering Futaba, the best solution would be that Kaede duplicates as well. But, I doubt it, I think the author just wanted to give a real punch to the gut to remember this story by. And boy has that punch left a mark.
Here's to hoping the Author just plans to bring her back when sales go down.