[@Tyki]
Doing my own research, Lina is not from Final Fantasy, but rather she is the main character of Slayers. Having done my own little research I've ascertained her to be nearly planet-level. Her most powerful spell, Giga Slave, is said to have the potential to destroy the entire world if miscast. And if cast perfectly, would have ultimate and unlimited destructive capability. The imperfect version used by Lina turned an entire ocean into a lifeless sea of death in an instant. It has the drawback that it costs a massive amount of power, it isn't the kind of thing that can be used on repeat.

Ragna Blade similarly has massive destructive capabilities, capable of destroying massive tracts of land or killing godlike beings. While it is less powerful than Giga Slave, and is not Lina's original creation, it's still on par with some of the strongest introduced characters. I don't believe she'd be able to enter Tsubasa, for example, at least not without a decrease in power.