If the giant is indeed Surtr, then Tanaka could be the sword of Freyr, which is said to be able to fight on its own, and Freyr being affiliated with the Sun and Summer could explain the "burning side" of Tanaka. With this, Magni, Thor and Mjollnir, and the end of a world with giants, that's some Ragnarok there.
It feels more and more like the end, and a "full reset", Illya get separated from everything that changed her life : without Miyu and the Miyuverse, nor the cards, everything can go "back to normal" even if she cannot forget. Even Ruby and Sapphire no longer have a goal without cards, and could be lost, destroyed, or taken back by the tower or Zelretch. Illya could then go on, leaving those days behind her, like some kind of "graduation at the end of the story"... but far more sad and dark
I'd prefer that than some bullshit to get everyone back (alive) and happy. If it ever happens, it better be good, but at this point, Illya dying has more chances to happen than this I guess.