In the final confrontation with Homurabi, Ryuuko returns. Afterwards, Akira finds that he remembers and understands a few more things. One of them is why Shirogane has refused to make any more shin than him. Drama with Mild Angst, I-3, MANGA CONTINUITY, implicit spoilers post-32

Whenever Akira had changed in the past he’d been too occupied with, most usually, almost dying to notice before he was suddenly waking up again. This time was different. This time, Akira could feel it happening, like walking down a see-saw and reaching the fulcrum, the tipping point, when uphill suddenly became downhill and the world turned over.