Probably the ability to use heat and thereby MVP? Medium is, overall, the less-useful MVP alignment, especially because so many of the Medium MVPs are either done better by other classes (Osi, Dopple) or have drops that suck it hard (Moonie).
I'm assuming the small memo is used somewhere useful for leveling, perhaps Odin's? If not it would beg the question, why not have Solar map be Missy.
Grats on 99 though ^O^