This happens very late in the novel (as of 2023, it's part of the machine translation); a prominent antagonist is crushed semi-graphically between two stone doors as they close.
Characters under the age of 18 are frequently treated as adults in-universe. Descriptions of the main character are provided with intent to arouse the reader before he is 18.
There is extremely graphic onscreen child death of a VERY young child (approx. 3 years old); I would recommend skipping pages 245-246 of the official English translation for vol 2 if this would trigger or upset you; you won't miss any plot points. There is also a semi-graphic child death (of a teenage girl) in the Tianyin Pavilion arc (currently mtl).
YWX can potentially be considered a trans male character (the closest literary parallel I can come up with would be Mulan or Alanna of Trebond), but is treated as female by the narrative and all characters after being outed as AFAB.