A theory, but hear me out: In order to unlock the hidden character, you have to play all the other routes first, right? And currently, she's on all three routes and that could somewhat count as fulfilling that condition. Since the condition is filled, Akira finally started to regain his memory as a result. As for what this results in, hehehehe... Ando-sensei is also suspicious as hell. So, there could also be 2 hidden character.