yep, this is supported by the show itself.

look at the contrast between mutsumi upstairs (double-meaning...), and "mutsumi" with her parents. mutsumi herself is never in sackboy form; it's always mortis

morty's been there since young!

#アニメムジカ_ネタバレ感想 #アニメムジカ https://t.co/otouOdKEfG https://t.co/MGAIjkRcHp January 01, 2025

#アニメムジカ_ネタバレ感想

sakiko indirectly admitting she doesnt believe mutsumi is on her side anymore and she only has the world of ave mujica she herself created left... her expression after seeing mutsumis reaction... ☹️☹️☹️💔💔💔 https://t.co/NC4dW2TD2E January 01, 2025

LRT, Yuzumoon reintroduces herself:
She is Yuzuki Watase, VA for Mutsumi Wakaba *and* Mortis

#アニメムジカ_ネタバレ感想 January 01, 2025

#アニメムジカ_ネタバレ感想

as of episode 3, we're getting a much clearer picture of what "I do not fear death" may mean for mutsumi

allowing mortis to take control means she'll finally be able to rest, and to protect herself from how much she is hurt by the world around her https://t.co/v3MSSVAyah https://t.co/e9nssNC9HE January 01, 2025

#アニメムジカ_ネタバレ感想

wait, so if mortis is modeling herself after who sakiko used to be...

does that mean that the weak version of sakiko who "already died" has been, in a way, reborn? https://t.co/YTRvxIof32 January 01, 2025