So we've got a name. A Shiro. And that he was obsessed with Nino and he died somehow and Nino was conflicted between feeling guilty and relieved so he decided to cut his wrist if only to get rid of the overwhelming feelings he had.
And Aiba came to begged Nino to fight and begged his shadow to let Nino go.

There were more to it, I'm sure. And I'm in for another adventure!
Thank you for this!