……well now, I would have thought that it would be explained in the Wiki, but Thongboy's Glowing Magical Balls are not explained, or even touched at all. Maybe they're his answer to a weapon? I think he does still have the physical strength—as skinny as he is, he does have some nice muscle tone going on…

Yes, I've been looking. DON'T JUDGE ME!

…And Fridge Brilliance! It strikes!
That sword Terra's got? The one we don't even see outside of chase?
Notice the dagger she's got?

What's the betting that it's VI's Atma Ultima Weapon? Its size and power varied with HP levels, going from the size of a dagger to a fricken buster-sword sized thing...and Terra can equip it!