User blog comment:Xilinoc/Ch. 600 - SNIPE/@comment-5693502-20141008195917/@comment-24153155-20141010075421

Lol! I never really thought about zanpakuto rusting. But since they resemble katana, leaving a Japanese sword to rust would be a no-go. In former days (some) Samurai caught toads on the 15th of August, dried the skin, rubbed the katana blade with the skin and left it to soak in oil overnight. It was believed that it would make improve the sword cut.

I like the idea of the world-breaking zanpakuto!