They did this because she was mentally unstable, perhaps because her power was too great.

The young older sister, quickly and certainly, had to teach her mentally unstable sister not to use her power.

When she did use it, she would display violence.

She could only become a target of fear for the younger sister.

We have both grown taller, haven't we?

Our powers have grown stronger as well.

You are about strong enough to destroy Gensokyo now...

But if you destroy this place we have finally drifted to...

There will no longer be anywhere that will accept us.

We vampires do not have reasons to entangle our destinies with others'.