If I don't use it, it should stay the same. My teammates at home... Joe and Clara, they've had kensei eyes for a long time, and they keep fighting. And Hayato-san's is degrading too, only he can't walk because of what it did to his leg. It's different for everyone.
But my core's already been used by two people before me; that's not normal. Nanami-san boosted my core at home when the lights started to dim... but of course that was months ago, now. I didn't know it could happen until a few weeks ago when I took a memory. And I've used it a lot here, so...