If anybody's wondering: To open the security doors, you need to progress the story (to-do objectives at the bottom of the HQ screen) until you recruit the green haired catgirl.
She's the one who enables you to open them. You don't need her in your 4-members battle team to do that, just have her recruited in your gang.
She's the one who enables you to open them. You don't need her in your 4-members battle team to do that, just have her recruited in your gang.