We created Transdeathnotesource (also called it TransDNsource) specifically for a headmate who's a Soul Eater Xive (so, a headmate who is cissouleatersource).
While most of us aren't keen on using source terminology, Liz has always had an affinity for more psychologically-based terminology but had usually been a bit confused because Liz would be referring to themself as a death note (fictional) introject, a death note fictive, or something similar, and then back themself up and ask themself: what the fuck? I've known Patti and Kiddo all of my life I'm not from Death Note.
That plus the time they imagined themself in front of a deathnote kind of sealed it for us yknow?
All of this is a super long way of saying: it just is. There isn't really a reason for it, that's literally just how Liz is, and that's okay. Liz doesn't need to have a reason to be a non-gender transid. This is what transplurality looks like in a cisplural...because transplural may not always mean transitioning specifically to become plural.