>>49644915
I'm not a lore expert, I just read some stuff and asked about undead before to understand what I was playing.
IIRC all the sister stuff is a way for sisterless loosers to retroactively fuck the universe into always having a sister by by reading her diary. Cat sister, shark sister, sister sister - all should work the same, but don't quote me on that.
Again, if I remember correctly, some sister-obsessed scientist long time ago lost his sister and quantum fucked the universe for this weird voodoo to work.