>>49883554
You just have to spread rumours. One half of the Longinus members can be obtained by spreading rumours that 'the Last Battalion consists of beautiful women', while the other half of the Longinus members can be obtained by spreading rumours that 'the Last Battalion are piloted by machine maidens', pretty much. In any case, you can only grab 4 Longinus members per round, and some of the Longinus members are actually male. Unless they changed all this completely with Tensei-P? The JP wiki seems to suggest that only one of them remains male with the rest of them being female. Certainly in one of the fights where all the enemy Longinus members were listed as male (in the battle screen), grabbing one of them still resulted in a female Longinus member. The translated text for Longinus 1 seems to indicate that when the translation was done, Longinus 1 was male (or else it's one of those funny translation mistakes). No, Longinus 1 doesn't have TS exp or anything.

But well, there's no such character named Hitler in eraMegaten. There is a man named the Fuhrer who survived the ending days of WW2 by faking his death that you fight, though. While you don't have to fight the Fuhrer, the Persona 2 endings do require you to go for them while ignoring every other ending, because it has the [No Other Ending] and [No Endless Mode] flag, so it also means that you can only go to NG+ after. But if you clear the last dungeon after having cleared another Ending, nothing happens and you continue your current round as usual.