Being 13(?) With a height of 154cm with a weight of 38kg. That menas that her bmi is 16. Which, luckly does mean she's in a healthy bmi range FOR HER AGE.
But it's really fucking low, 36.4kg is the line under whoch you become underweight at that age. And keeping the 38kg into adulthood, lets say...
To Anyone confused about if Shu is a woman or guy. Look at her in the last panel of the last page.
Those are boobs. Based on the fact that we can see them, we can assume a gender identity that's okay with having boobs like that and not binding them so that the chest is flat. Therefore. Woman.
Oh, I think I'm pretty sure that that core already bit back. I think it belonged to the ancient cultivator whose dream/memories her brother was stuck in.
Since, it is what A-ting used against the sickly evil guy. And the sleep her brother fell in followed immediately after her attack iirc.