For the 2nd arc, he's rumored to be the pilot of the xvm-dgc Khronos. The "dgc" in its model code supposedly stands for "Decil Galette Custom".
Not sure if these are accurate. Vagan MS model designation:
First letter
o - mass-produced
x - not mass-produced (one-of-a-kind or custom)
Second letter
v - Vagan
Third letter
v - transformable
m - non-transformable
d - optional equipment
Second part of model designation
f - fighter?
a - assault / attack?
e - optimized for Earth/planetary use?
xc - for X-Rounder use
xcr - for X-Rounder use (remodeled / revision)
xd - for X-Rounder use (optional equipment?)
gz - Gira Zoi
zgc - Zeheart Galette custom
dgc - Decil Galette custom