I think the 'white pen named hope' is the SOUL. We glow pure white during that staircase scene, and I think that there's a line about the SOUL having hope during the Titan fight. So Susie will probably have to come into contact with the SOUL at some point. When she dunks Kris into the Titan's eye cavity, both of them sort of 'orbit' the SOUL, as if to suggest both will be related to it.