Solved by Walking. Nagi/Mamoru, lots of identity stuff in the beginning.

Viridian has some telepathy/identity fic: "Halber Mensch" has Schuldig, "Unguarded" is about Omi, "Guests" is twisted and wrong and quite funny.

My hereness, your thereness is caught between Mamoru and Omi.

Reunion has Mamoru and amnesiac Yohji.

And I wrote some stuff: You Can Call Me Al, where Schuldig gets confused and decides he's someone else for a bit;

Destruction and Repair is about a rather messy situation overall.