“My body isn’t strong enough to last outside. When I told you that I had no interest in the world – I meant it, but there’s more to it. I fear the air on the mainland would be too rich for me. And my brother – worries about me.”
By now Nanami’s weak constitution must have been apparent to Togame. The sister was fragile – even brittle.

Katanagatari Omnibus 1, Page 47