Summoner
Some thought that a trigger event was the traumatic part of getting powers.
In her case, it was the "vision" that followed.
Having lived thousands of years through the eyes of a hundred and more legends from another world, all in mere seconds, chosen through naught but mere happenstance during the death throes of a far distant reality, she found herself the bearer of uncountable beasts and monsters, men and women, abilities and spells, all borne from fantasy, yet far too real to ignore or pretend they did not once exist.
In the aftermath, she starts to realize that no matter how much she tries, a normal life on Earth Bet is impossible, not with what she's become, what she can do. The people she can help.
Inevitably, the walls lengthen, the bars thicken, the shackles tighten.
Undaunted, beaten but unbowed, she resolves to drag Earth Bet to a brighter tomorrow, no matter how much it kicks and screams on the way there.
Whether she can succeed is another matter entirely.
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(No knowledge of LoL is needed, but would help. There will be variation in how champions/mechanics work for realism. Story starts up a little slow but quickly ramps up to a frenetic rollercoaster.)