Niu has... the reverse answer, but close enough. Willing to call it here due to risk of confusion if I didn't acknowledge it. It's not Flammie, but it is the identical-looking Mana Beast.
1. Can't say I'm a fan of technology. Or at least that specific piece of it. - The ancient society that got smashed had modern technology, and more specifically it wants to destroy the Mana Fortress which is busy draining mana from the land.
2. Unlike my relative, I certainly won't serve those unworthy people. - Unlike Flammie, the Mana Beast is pretty much going to destroy civilization.
3. Man, that tree spells trouble for me. - You need to use Mana Magic from Dryad ("spells", har) on the Boy to beat the Mana Beast. As far as "games with trees," I was hoping that some people might think of the Mana Tree, even if that wasn't actually the right tree here.
4. I can affect the weather. Only once, though. - The Mana Beast turns into snow after it dies.
5. Anarchic Entity Lezard is a wuss compared to my magnificent defense. - Lezard merely reduces non-Valkyrie damage to 10%. Most everything that isn't the Mana Sword just bounces off the Mana Beast (though you can mildly scratch him with a lvl. 9 Spear powered up by Moon Energy or the like).
(unused) 6. Bang that drum all you like - you won't enjoy the ride I give you. - The official "make it obvious" clue if things had continued.
I will say I was amused by the Suiko4 guesses; I'd forgotten Graham Cray's mighty "turn self into an evil tree" rune. Also, Fou-Lu fits pretty well too, now that I look at it.
You're up, Niu.
