Pretty sure it was used for the first song of the encore (to avoid giving setlist spoilers), so most likely an unique use unless the song actually comes back in the future setlists (after “Kanshasai vol.2”, that is). Metal Mickey: yes, that's due to the tuning, tuned half a step down.
And as far as I remember the guitar that MAMI used in that case was her signature Squier. People who attended the gig, can you confirm it was that guitar, or was it another ?