a certain dark hero

Touma kamijou vanishes for a whole three months out of thin air... but then reappears not willing to answer what has happened but mikoto misaka notices that Touma is darker and no longer caring and heroic as he used to be. Misaka notices that the darkness in Touma is much stronger and deep than it appears on the surface. and with it Mikoto finds out that Touma has been hiding a new power but how was it obtained? she also see's something else has changed in Touma and its almost .... demonic