Did you know? 

The gem that was first introduced in Alone as the key to the Abyss was originally and has remained the only way to open it, through Shintaro (Brethren). 

When the Abyss was created, my sister and I at first didn't really know what to do with it. After a bit, it became its own separate realm, and the only way to open the gates was through a Dark Key that was hidden away. Only Shintaro (Brethren) knew where it was, and he didn't plan on telling anyone where he'd hidden it.