What lore do you ignore?

[Cleretic]

but it was stated by matoya that by useing that ability she is actively shortening her lifespan(prolly do to being sundered since emet didnt seem to have that issue). so prolly doesnt always have it active. this was all stated in the .x section of HW if i remember right.

Actually this is a bit of a misconception from the English translation. She's not shortening her lifespan, she's just consuming more aether. Matoya's concern in other languages is less like if she was actively reducing her lifespan and more the sort of concern parents get when they learn their child's started driving a motorcycle. English wasn't as clear on the severity of things as the Japanese translation, so we got some wires crossed.

The 6.2 stuff with Zero is sort of quietly righting the ship on this one; aether can be replaced, and Y'shtola's happy to run on a less-than-full tank. It's not an active danger and it's not actively reducing her lifespan; she just has to take more care of herself than your average person, probably eat more than she used to.