How does each champion's gameplay fit in with their story in your opinion?
I'm a little biased but for me Katarina fits so well with her lore. She betrayed her orders and snuck into the enemy camp to kill their commander, but his death just rallied the enemy troops, and the second-in-command led a charge into her father's army encampment and cost them so many casualties.
In game her playstyle fits so well. The true mark of a Katarina player is when you're flanking behind the enemy team and your team is spam pinging:
You betray your team's orders: fall back, caution, caution, fall back, caution, danger, danger!
TRIPLE KILL
Enemies are mi- Enemies ar- Ene- En- Enemies are m- Enemies are missing????????????
Then your team is like "sweet lets fight!" and the fed Jax kills them 1v4 while you're recalling.
XD

and
1v2
In game: dies to whatever manages to get close
Although in the Taliyah/Sivir story he is close to in-game: people don't fight him, they scream, run, dodge whatever magic is falling from the sky and eventually either die or run away
m00nd0 tink u a bug zizzy