yes, mason is! though her relationship with gender is largely insecure and a little complicated, especially at the age she's depicted in the ref. she's something more of a boy/girl with her more masculine & brotherly traits also being emphasized, especially for sophie who interchanges how she genders mason based on very cute and arbitrary reasons. mason grows more into his femininity when she's older which also helps her be more relaxed with her masculinity. she spends a large amount of time taking care of and being sophies Older Brother. later in life still in the close company of sophie, she gets to be treated more like the baby sister that she is