Maybe there's connection with PUPu.
Remember PuPu gives us something(PuPu card)
PuPu card can be refined into Aegis Amulet.
Aegis Amulet can be used as Eva-J or Speed Up
Maybe because of Aegist Amulet Squall and Co can survive at TC
Maybe this is the answer,maybe not,who knows...
Indeed. So if we dun do the PuPu sidequest ALL YOUR CHARACTERS will be wiped up in Disc IV in regardless of age and sex.