For those who have beaten the game, a couple of questions about Symphonia and Phantasia

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How does the ending relate back to Phnatasia? I've never played the game but I was wondering about how Dawn of the New World ties Symphonia and Phantasia together. (I have watched the Phantasia OVA, but that doesn't really count, does it?) For starters, whatever happened to Ratatosk when Dhaos began his attack on Midgard, and why was Martel on the verge of death? Didn't Ratatosk re-program the world so that nothing would be reliant on mana anymore? Ratatosk did mention that it was only a matter of time before humans destroyed the tree again... I'm not sure whether he was just being pessimistic or was foreshadowing what happens in Phantasia.

Any explanations would be appreciated :D