How much were the DLC characters in Japan? Might get them if they're unique enough/have their own story or cutscenes.
650 yen and they don't have their own story but their gameplay has certain details exclusive to them.
See, the Extar/Liberator mechanic was tweaked with them so they would remain faithful to the anime's rules. Thus, Mirei and Mamori
can't switch roles nor pick different partners (effectively making them a single character). But while all the other girls have four different upgrade levels, Mirei always begins the stages already on the first drive. Again, to remain faithful to the anime since Mirei's default weapon is Mamori.
This serves to balance Mirei, she begins the stage with a notable advantage but she can't change her stat bonus like the other girls do.
There's a lot of care put on Mirei, her animations are also filled with references to the anime, with many poses and attacks being lifted straight from the anime or from promotional materials and her music theme (in my opinion the best song in the game) being a pretty awesome arrangement of the anime's OP.